VCE Chemistry Unit 4

chapter 23

chapter outcomes

key knowledge

22Fossil fuels

comparison of energy sources: types, uses and sustainability, including brown coal, natural gas, nuclear fi ssion and biochemical fuels

After completing this chapter, you should be able to:

describe types of fossil fuels, their uses and sustainability

distinguish between renewable and non-renewable energy sources

use social, economic and environmental factors to compare common energy sources

assess the suitability of various energy sources for particular situations

explain how energy conservation and consumption affect the sustainability of energy sources.

2333333332323Fossil fuels 367

23.1

Energy sources todayHuman history becomes more and more a race between education and catastrophe.

H.G. Wells, The Outline of History (1920) vol. 2, ch. 41, part 4

How much energy do we use?Energy is measured in units called the joule, J. Larger amounts of energy are commonly expressed in kilojoules, kJ (1 kJ = 1000 J), or megajoules, MJ (1 MJ = 1 000 000 J). A petajoule, PJ, is a useful unit for discussing national energy needs: 1 PJ = 1 1015 J.

A person in a huntergatherer society uses approximately 10 MJ of energy per day. Despite being less active than huntergatherers, each person in our modern industrial society uses, on average, nearly 1000 MJ per day. This fi gure is one hundred times greater than the bodys basic requirement. The bulk of our energy use is for transport, heating, and domestic purposes (Figure 23.1).

The national energy budget is somewhat higher than your personal tally. Australia uses about 2000 PJ of energy per year for mining, manufacturing, construction, commercial services, farming, fi shing, forestry, and residential use.

World energy consumption is around 4 1020 joules per year. Some nations could be considered gluttons in terms of their energy consumption. The United States consumes a quarter of the world energy pie. Australia is just under the US on consumption per head of population (Figure 23.2). The worlds poorest nations are starved of food and energy.

chemfactIn our society, about 10 J of energy is expended on production, processing and distribution to provide 1 J of food.

Transportation(47%)

Heating(40%)

Other includingrefrigeration, electrolysis

(4%)

Lightingand motors

(7%)

Cooking(2%)

Figure 23.1Use of energy in Australia.

Figure 23.2Energy consumption per capita (2004). Energy use in the world is far from equal. Source: BP Statistical Review of World Energy, June 2005.

Consumption per capitaTonnes oil equivalent (toe)

01.5

1.53.0

3.04.5

4.55.0

> 6.0

toe per capita

368 23222232322222332322233Supplying and using energy368

Meeting our energy needsBurning wood (and in some countries, dung) was the dominant method of obtaining energy up to the middle of the nineteenth century. Wood supplies once seemed inexhaustible and, like fossil fuels today, satisfi ed most of the demands of the time. The clearing of forests and an increasing demand for fuel to operate machines led to the transition from wood as a source of energy to coal and oil.

The fossil fuels coal, oil and natural gas provide nearly 90 per cent of the worlds energy needs. As members of a society that is heavily dependent on fossil fuels as a source of energy, it is sometimes hard for us to imagine obtaining energy from elsewhere. Feasible alternatives to fossil fuels are not always easy to fi nd. In Chapter 24 we briefl y consider some existing alternatives and look at what the future may hold in terms of our energy supplies.

The dominance of fossil fuels as an energy source occupies only a brief part of human history. There is growing pressure to reduce our future dependence on these fuels for several reasons, of which the main ones are: increasing concern over the effects of gases released into the atmosphere

as a by-product of the combustion of fossil fuels. In particular, carbon dioxide contributes to atmospheric warming (the greenhouse effect) and sulfur dioxide is known to cause acid rain (p. 252)

appreciation that fossil fuels are non-renewable: world reserves are limited and will eventually run out

demand for petroleum as a raw material for polymers, paints and other petrochemical products.The pressure for change was fi rst felt strongly during the oil crisis of the

early 1970s, when several Middle Eastern oil exporters restricted production for political reasons. The effect of their actions on the price of oil is shown in Figure 23.4.

The rising cost of oil during the 1970s prompted greater interest in other energy sources. Nuclear energy became more attractive economically. Research into alternative sources of energy such as solar, wind, tidal power and biochemical energy was encouraged, and more effi cient ways of using oil were developed. Much of the research and development resulting from the

Figure 23.3World energy consumption, 1860 to 2005, with projections to 2020.

New technologies

Nuclear energy

Natural gas

Oil

Coal

Hydraulic power, wood, windEne

rgy

1860 1880 1900 1920 1940 1960 1980 2000 2020

233333232 Fossil fuels 369

100

90

80

70

60

50

40

30

20

10

0

1851

-69

1870

-79

1880

-89

1890

-99

1900

-09

1910

-19

1920

-29

1930

-39

1940

-49

1950

-59

1960

-69

1970

-79

1980

-89

1990

-99

2000

-04

Pennsylvanianoil boom

Russianoil exports

begin

$ 2006

Sumatraproduction

begins

Discovery ofSpindletop,

Texas

Fears ofshortagein USA

Growth ofVenezuelanproduction

East Texasfield

discovered

Post-warreconstruction

Loss ofIranian

supplies

Suezcrisis

YomKippur

war

Netback pricingintroduced

Iranianrevolution

Asianfinancial

crisis

Invasionof Iraq

IraqinvadedKuwait

?

?

?

?

Figure 23.4Changes in the price of oil.

oil crisis is ongoing. The 1991 and 2003 Gulf Wars in the Middle East and the subsequent political instablity in this region, where most of our planets oil reserves are found, has continued to force up the price of crude oil.

23.2

Energy convertersConversions of energy to one form to another involves losses, usually in the form of thermal energy.

Device Energy transformation Typical effi ciency (%)

Steam turbine Thermal to mechanical 45Gas burner Chemical to thermal 85Galvanic cell (battery) Chemical to electrical 6090Fuel cell Chemical to electrical 50Generator Mechanical to electrical 90Solar cell Light to electrical 1014Hot-water heater (electric) Electrical to thermal Nearly 100Electric motor Electrical to mechanical 6090Petrol engine Chemical to mechanical 2025Hydrogen engine Chemical to mechanical 2550Fuel cell powered vehicle Chemical to electrical to mechanical 2030Photosynthesis in leaf Light to chemical 1

TABLE 23.1 Effi ciency of energy converters

The engine in a car is an energy converter. It converts the chemical energy in petrol to thermal energy, by combustion. Petrol is mostly octane (C8H18). The combustion of octane is a redox reaction:

2C8H18(l) + 25O2(g) 16CO2(g) + 18H2O(g)

chemfactOne litre of petrol provides about 34 200 kJ of energy when it is burnt in the engine of a car.

Figure 23.5Energy transformations in a car. Only a small proportion of the chemical energy in petrol is converted into motion; most is converted into heat.

33 J lost as heatthrough exhaust gases

30 J lost as heat throughengine cooling water

5 J lost by pumpingcombustion air

7 J lost to engine friction

5 J accessories

20 J topropelthe car

100

J of

che

mic

al e

nerg

y in

pet

rol


23.3

Fossil fuelsNon-renewable resources are those that are used at a rate faster than they can be replaced. Fossil fuels and uranium are fuels of this type. There are fi nite reserves of these which can eventually be exhausted.

There is obvious confl ict between using non-renewable resources and sustainability. Sustainability is all about meeting the long-term ongoing needs of society, as well as immediate and short-term demands. This concept includes care of the environment as well as the economic and social wellbeing of future generations. In a United Nations report, sustainable development was defi ned as meeting the needs of the present without compromising the ability of future generations to meet their own needs (Our Common Future (Brundtland Report), Oxford University Press, 1987).

About 80% of Australias electricity is generated from burning coal. Gas-fi red and hydroelectric plants generate about 10% each. The sources of electricity generated in Victoria are shown in Table 23.2. Despite enormous uranium reserves, Australia does not have nuclear power plants. The Victorian government rejected a proposal in the 1960s to build a large nuclear plant on French Island in Western Port Bay. Increasing world oil prices and pressure to reduce greenhouse gas emissions may lead to a rethink on nuclear options for Australia.

Relative electricity generation by fuel source in several developed countries is shown in Figure 23.6.

Source Megawatt Percentage Cost per megawatt hour ($)Brown coal 6395 62 3140Gas 1505 14 4247Hydro 2325 22 4555Wind 238 2 7080

TABLE 23.2 Victorias electricity sources (2006)

The Age, 5 August 2006

Coal, oil and natural gas formed from primitive plants and animals. When we burn these fuels we are burning the remains of plants and animals that were alive millions of years ago. The plant and animal material has undergone complex changes while buried under tonnes of mud and sand, but it still retains the chemical energy the plants originally accumulated by carrying out photosynthesis. Chemical energy in fossil fuels can be considered as trapped solar energy.

Only about 20 to 25% of the energy released by the combustion of petrol is transformed into mechanical energy and used to move the car. In other words, more than 4 J of chemical energy is needed to obtain 1 J of mechanical energy. Most of the waste is transferred through the exhaust and the cooling system to the outside air as waste heat (Figure 23.5).

Figure 23.6Electricity production by fuel source. The size of the block represents a regions energy use. Energy use in the world is far from equal. Source: Nuclear Energy Prospects in Australia, Nuclear Issues Briefi ng Paper 44, April 2005, Uranium Information Centre Ltd.

100

80

60

40

20

0

Per

cent

age

S. Korea281

Japan1033

Canada588

USA3864

OECD Europe3258

UK393

Aust2172001 TWh:

NuclearOil

GasCoal

Hydroand other

23333333323223Fossil fuels 371

CoalAs wood and other plant material turn into coal, some gradual chemical changes occur. Wood is about 50 per cent carbon. As it is converted into coal, the carbon content increases and the proportion of hydrogen and oxygen decreases. The wood progressively becomes peat, brown coal (also called lignite) and then black coal or anthracite (Figure 23.7). Coal is a mixture of large molecules made from carbon, hydrogen, nitrogen, sulfur and other elements. The relative molecular masses of these molecules can be as large as 3000.

The amount of water in coal decreases as these changes occur. When coal is burned, energy is used to vaporise this water, reducing the amount of heat released. Black coal, which contains least water, is therefore a better fuel than brown coal or peat. Although black coal is usually buried further underground, its higher heat value often makes mining worthwhile. Large brown coal deposits are located in the Latrobe Valley in Victoria. The power stations located next to the open-cut mines burn brown coal to generate electricity.

Uses of coal

Over three-quarters of Australias electricity is produced in coal-fi red power stations. You may indirectly be burning coal when you switch on an electric heater, use a hair dryer or watch television. Rather than cart coal to every factory, offi ce and household, the chemical energy in coal is converted to electrical energy at a power station. Electricity is easily transmitted and is a convenient and versatile form of energy, but it is no cleaner than the energy source used to generate it.

The reaction that occurs when coal burns can be written as:

C(s) + O2(g) CO2(g)

This equation is a simplifi cation of the actual reactions that occur, since coal is not pure carbon. Signifi cant quantities of ash are formed, as well as water vapour and sulfur dioxide. Oil and natural gas, by comparison, are cleaner burning fuels, producing less smoke and fewer pollutants.

chemfactPeat is not an important fuel in Australia. It is still dug by hand from the surface of boggy ground in parts of Ireland and Scotland where the traditional right to dig peat is retained within families. A smoky peat fi re was an essential energy source for some of our ancestors, and is still required for the manufacture of whisky.

chemfactThe generation of electricity by power stations using brown coal generates 1.7 tonnes of CO

2 per megawatt hour of

electricity produced. Power stations fi red by black coal produce 0.9 tonnes of CO

2

per MWh, while those that use natural gas produce 0.6 tonnes of CO

2 per MWh.

Figure 23.7Steps in the formation of coal. Values of the carbon content and heat released upon combustion are for dried coal.

Peat60% carbon

Heat released 25 kJ g1

Brown coal70% carbon


Black coal90% carbon


Decayingvegetation

Incr

easi

ng q

ualit

y as

fuel

Increasing time, p

ressure, temp

erature

Figure 23.8Mining brown coal in the Latrobe Valley.


Research is being conducted on means of reducing the carbon dioxide emissions, possibly by means of underground storage (geosequestration). A new brown-coal densifi cation process may be in place in the Latrobe Valley in the next few years. This is a type of power station that will generate electricity while converting much of the carbon in the brown coal into gas and coke. The gas will be used in the generation of electricity while the coke can be sold for steel-making both within Australia and for export. While it is not a perfect solution, the process does reduce overall carbon dioxide emissions.

Coal-fi red power stations

A number of energy transformations are involved in a coal-fi red power station (Figure 23.9). Coal is burntchemical energy in coal is converted to thermal energy. Heat from the burning coal is used to boil waterthermal energy from

burning coal becomes thermal energy in steam. Steam is passed through a turbinethermal energy in the steam becomes

mechanical energy as the turbine spins. Electricity is produced from a generator that is driven by the turbine

mechanical energy is converted to electrical energy.

Figure 23.9a How a coal-fi red power station works and where energy is lost.b Energy conversions in the power station.

Flue gas

10% of the coal's chemicalenergy is lost as heat in thechimney gases

Chimney Steam

5% of the coal's chemicalenergy is lost in miscellaneous

ways in the power plant

TurbineGenerator

Electricity

35% of the coal'schemical energyis convertedto electricity

50% of the coal'schemical energy is

lost as heat in steam

Chemical energyin coal

Thermal energyof burning coal

Thermal energyof steam

Mechanical energyof turbine

Electrical energyfrom generator

Boiler

Coal

Pump

PumpCondenser

Cooling tower

(a)

(b)

a

b

23333332322 Fossil fuels 373

Figure 23.11Australian coal-producing basins.

Figure 23.10Water vapour rising from steam-cooling towers at Victorias Loy Yang power station shows that energy conversions are less than 100 per cent effi cient.

The most ineffi cient transfer of energy occurs when thermal energy in the steam is transformed into mechanical energy by the turbine. Overall effi ciencies of about 30 to 40% are achieved. While this fi gure does not sound impressive, it is greater than the 25% effi ciency of the car engine.

Coal reserves

As you can see from Table 23.3, there are large reserves of coal remaining in the world. Estimates of reserves are continually changing as new deposits are located and mining of less accessible deposits becomes economically viable. Australia is fortunate to have large deposits of coal, and exports more than any other nation.

Fossil fuel Size of reserves (tonnes) Life of reserves (years)Coal 1 1012 250Oil 1 1011 40100Natural gas 1 1011 4575

TABLE 23.3 Estimated global fossil fuel reserves and their lifetime at current production and use rates (2004)

Coal represents about one quarter of the fossil fuels consumed around the world and it is anticipated that this fraction will increase greatly as reserves of oil and natural gas diminish. Coal is likely to become more widely used than oil in the future.

A number of methods for converting coal to liquid and gaseous fuels have been demonstrated. In fact, coal-to-oil conversion was employed in Germany during World War II when the Germans were unable to import oil. A process known as fl ash pyrolysis has been developed by CSIRO for converting coal to oil. Pulverised coal is heated to 600C. A tar forms that is reacted with hydrogen to give a type of crude oil.

These processes may well offer economic alternatives in the future.With growing global awareness of global warming, Victorias brown coal

industry has faced the challenge of reducing emissions of the greenhouse gas CO2. Victoria has set up a research centre to develop cleaner burning technologies.

chemfactThere have been proposals to store carbon dioxide produced by power stations and other industries deep underground in depleted oil and gas basins. This process of isolating the CO

2 is often described as sequestering

the CO2 or carbon sequestration. A trial

sequestration was conducted in south-west Victoria in 2007.


OilCrude oil (petroleum) is a mixture of hydrocarbon molecules that are members of the homologous series of alkanes. Crude oil itself is of no use as a fuel, but many of the compounds in it are.

The relative amounts of alkanes in crude oil from different sources vary. Oil from Bass Strait, for instance, contains relatively few of the larger molecules needed to form lubricants and bitumen. As a consequence of this, Australia imports oil to blend with the oil it extracts locally.

Fractional distillation of crude oil

Separation of the components of crude oil is accomplished by a process called fractional distillation, which is performed in a fractionating tower (Figure 23.13). The oil is separated into several fractions, each containing a number of hydrocarbons that have similar boiling temperatures.

Oil entering the fractionating tower is fi rst heated to about 400C so that it becomes a hot mixture of vapour and liquid. On entering the tower the liquid and vapour immediately separate and the vapour rises upwards through the tower.

The temperature in the tower decreases gradually with increasing height. Within the tower there are horizontal trays, each containing hundreds of bubble caps. These impede the upward movement of gases (Figure 23.13). As the vapour rises it forces the caps up and it bubbles through condensed liquid in the trays. Those substances in the vapour that have boiling temperatures almost equal to the temperature of the liquid in the trays condense and are collected. Consequently, fractions collected from trays higher in the tower will be those with lower boiling temperatures.

Oil and gas basinsResources are shown as a percentageof total resources. estimated Australianresources as at 1 January 2003Gas = 167,285 PJLiquids = 32,601 PJ(Geoscience Australia 2004)

Coal basins

Uranium mineral deposit

Operating uranium mine

Oil basin: producing

Oil basin: not producing

Gas basin: producing

Gas basin: not producing

Coal basin: producing

Perth Basin

Perth Basin

ArekaringaBasin

Leigh Creek

Collie

Laura Basin

GalileeBasin

Bowen Basin

Callide Basin

Maryborough Basin

Tarong Basin

Moreton Basin

Gunnedah Basin

Gloucester Basin

Sydney Basin

Oaklands Basin

BacchusMarsh

Anglesea

LatrobeValley

Fingal

Surat Basin

Carnarvon Basin

Amadeus Basin

Browse Basin

Bonaparte Basin

Cooper/EromangaBasin

Adavalle Basin

Bowen/SuratBasin

Gippsland BasinBassBasin

Otway Basin

HOBART

MELBOURNE

SYDNEY

BRISBANE

DARWIN

ADELAIDE

PERTH0.6%

0.8%

55.7%

49.7%

18.3%

16.0%

18.6%

16.9%

0.1%

0.1%

10.9%

5.1%

1.89%

0.4%

1.0%

0.2%

WOLLONGONGPORT KEMBLA

Figure 23.12Australian oil, gas, coal and uranium fi elds.

23333333323223Fossil fuels 375

The boiling temperature of molecular compounds depends on the strength of intermolecular forces. Attractions between non-polar alkane molecules arise from weak dispersion forces, the strengths of which increase with molecular mass. As a result, each fraction consists of alkanes within a specifi c mass range. Lighter alkanes condense near the top of the tower, whereas heavier ones condense near the bottom. The composition, boiling range and use of each fraction is summarised in Figures 23.13 and 23.14. The naphtha fraction that boils (and condenses) between 110C and 180C, for example, consists of alkanes containing between 6 and 10 carbon atoms, that is, C6H14 to C10H22.

The liquid remaining in the bottom of the tower contains hydrocarbons of high molecular mass. This residue is normally distilled again at reduced pressure to separate its components.

The exact operating conditions and fractions separated in the fractional distillation process vary from one refi nery to another, depending on both the source of the crude oil used and market demands. Fractionating towers operate continuously and may be designed to accommodate a number of different feedstocks, such as Bass Strait crude oil or crude oil from the Middle East, which is richer in the heavy fractions.

Catalytic cracking: producing lighter hydrocarbon fractions

The process that gives rise to more small alkane molecules is catalytic cracking, using a zeolite catalyst made of aluminium, oxygen and silicon. A catalyst is a substance that changes the rate of a reaction. The presence of the catalyst allows cracking to be performed at relatively low temperatures (450500C) and provides good control of the range of products formed. The catalyst is a fi ne powder which is in a fl uid-like suspension in the fl ow of the hydrocarbon gases. Higher quality fuels can be produced by this process. A typical reaction occurring during catalytic cracking is:

C29H60(g) C8H18(g) + C8H16(g) + C13H26(g)

The products from fractional distillation of crude oil do not necessarily match the fuel needs of society. They are often defi cient in the proportion of lighter fractions needed for transport fuels, and contain much greater proportions of the residue fractions required for production of paraffi n wax, lubricating oils and bitumen.

Figure 23.13Fractional distillation of oil.

Bubble cap

Crude oil

340oC

260oC

180oC

110oC

150oC

Fractionating column

Refinery gas(C1C4)

Gasoline(C5C6)

Naphtha(C6C10)

Kerosene(C10C14)

Gas oil(C14C20)

Bitumen(larger than C20)

Heater

chemfactZeolites are substances that occur naturally in volcanic rocks. They have a sponge-like structure, with minute channels running through them. By modifying the size of these channels in synthetic zeolites, chemists have developed useful catalysts (Chapter 15).


Cracking breaks up (cracks) larger alkane molecules into smaller alkanes as well as producing small alkene molecules, such as ethene, together with hydrogen. The alkenes are such useful substances that they are deliberately produced in large amounts. Chapter 22 discusses ethene production in detail.

Molecules such as octane (C8H18) are a major component of petrol. The process also yields larger alkanes and alkenes that can be used as a feedstock for thermal cracking furnaces to produce more ethene.

As well as being used for fuels and lubrication, some of the hydrocarbons are used as solvents, and signifi cant proportions are converted into alkenes to be used as the starting point for the enormous range of polymers, plastics, dyes and pharmaceuticals that we rely on. When investigating the sources of fuels for the future, we must also think about how to obtain molecules that can be converted into all of these other useful substances.

Uses of crude oil

The various products obtained from the fractional distillation of oil include fuels such as petrol, kerosene, diesel and liquefi ed petroleum gas (LPG). Other products obtained from crude oil are used as raw materials in the manufacture of a range of products from plastics to pharmaceuticals.

Liquefi ed petroleum gas (LPG) has replaced petrol as the fuel in over 500 000 vehicles in Australia. Most of these vehicles are taxis or trucks, or are fl eet-operated. LPG is predominantly a mixture of propane and butane. It is expected that it will be available for at least the fi rst half of this century, as it is obtained in signifi cant quantities from local oil fi elds.

The major impediments to greater use of LPG are: the need for large gas tanks, which reduce space in the boot of a car the cost of engine conversion to allow its use actual and perceived risks of explosions from leaking gas limited availability in remote areas.

Conversion to LPG is likely to remain attractive as long as the price is signifi cantly less than that of petrol. In 2006 the federal government provided a fi nancial incentive for owners to convert their cars to LPG in response to community concern about rising petrol prices.

Figure 23.14Supply and demand for different fractions of crude oil.

Refinery gas: LPG, feedstock forchemical industry

Gasoline: Petrol

Naphtha: Cracking to petrol; chemical industry

Gas oil: Diesel; cracking to petrol

Kerosene: Jet fuel

Bitumen: Lubricatiing oil; bitumen; fuel oil

Crude oil

Supplyin oil

Demand forproduct

Siz

e of

mol

ecul

es in

crea

ses

23333332322 Fossil fuels 377

Oil reserves

Estimates vary, but world oil reserves are much smaller than those of coal and may last only for several decades (Table 23.3). More than half of these reserves are situated in the politically sensitive Middle East. Australias relatively small oil reserves are likely to be exhausted early this century (Figure 23.12). Importation of large amounts of oil would have a signifi cant impact on Australias economy.

Natural gasNatural gas is mainly methane (CH4) together with small amounts of other hydrocarbons such as ethane (C2H6) and propane (C3H8).

Natural gas is a popular fuel for home heating and cooking. As world oil prices increase, natural gas may increasingly replace petrol in cars and, in future, diesel fuel in many buses and trucks. The 510 MW Newport power station in Melbourne uses natural gas to generate electricity. Its city location near the mouth of the Yarra River provides water for cooling and minimises transmission lines to distribute the electricity.

Unlike coal-fi red power stations, the energy from a gas or oil-fi red power station can be increased or decreased quickly to meet changing demands for electricity over a daily period.

A gas-fi red power station operates in a different way from a coal or nuclear powered plant. In coal and nuclear power stations, heat is used to produce steam that drives turbines that turn generators. However, steam is not used for spinning turbines in a gas-fi red power station. Instead, hot gases from combustion expand air in a combustion turbine, spinning propellor-like blades and an attached generator. Other differences are the source of heat energy, how the energy is released, and how wastes are managed. About one third of the energy released from combustion drives the electric generator. Gas is simply burnt in air to to release mainly CO2 and H2O and heat energy.

The amount of CO2 released per MW of electricity by gas-fi red plants is half that of coal-fi red plants. Unlike coal in Victoria, the combustion of gas produces fewer pollutants such as smoke particles and sulfur dioxide, a precursor of acid rain. Smoke particles can be a signifi cant pollution problem because particles smaller than 10 m are small enough to enter our lungs, increasing the risk of heart and lung disease including cancer.

Figure 23.16Newport Power Station, Melbourne.

Figure 23.15A geologist examines a sample of oil shale from a drill core. Vast amounts of this rock, which contains an oil-like material, are found in Australia and overseas. In future it may become economic to mine the rock and extract this oil.


chemistry in action

Environmental impact of Newport power station

Local fi shermen know that the warm water in Hobsons Bay next to the 100 to 500 megawatt Newport power station increases their chances of coming home with a catch. The gas-fi red power station draws water used for cooling and pumps it back into the shipping channel near the mouth of the Yarra River, causing an increased temperature of several degrees. The fi sh are usually black bream, mullet and tailor. Mulloway and pinky snapper are occasionally found in the hotties, as some locals call the spot.

Victorias Environment Protection Authority (EPA) specifi es limits for temperature, fl ow, acidity, iron, ammonia, chlorine, carbon, nitrate, turbidity and dissolved oxygen in the cooling water released from the Newport power plant. The plant operators expressed concern with dredging proposed in 2005 to deepen the channel to allow the passage of deep-water ships. Sediment containing high levels of sulfi de could corrode tubes in the power plant, forcing the station off-line with consequent power blackouts in Melbourne.

Reserves of natural gas

About 20 per cent of the worlds energy is obtained from natural gas. It supplies a similar proportion of Australias energy needs. As with oil, known reserves of natural gas are severely limited (Table 23.3).

Fossil fuels may cost the EarthApart from the limited reserves, there are other concerns about the use of fossil fuels.

Chemicals extracted from fossil fuels are used as the raw materials for many of the products of the chemical industry. Many of the materials that contribute to our current lifestyle, such as plastics, fi bres and pharmaceuticals, have originated from fossil fuels. Can we afford to use fossil fuels in transport? Can we afford to burn such valuable raw materials?

Both wood and fossil fuels release carbon dioxide and water when they burn. Increasing atmospheric levels of carbon dioxide and some other gases that trap infrared radiation contribute to the phenomenon known as the greenhouse effect that is increasing world temperatures.

The warming of our planet, associated rises in ocean levels and disrupted climates may be the long-term consequences of using fossil fuels.

Air Exhaust

Common shaft forturbine/generator

Pressurises air Spins turbineand generatorFuel

Generator

Figure 23.17Expanding gases drive the blades of a gas-fi red turbine.

2333333323223Fossil fuels 379

Governments and industry are exploring a number of possible energy sources for the future: production of biochemical fuels such as ethanol and biodiesel production of hydrogen from natural gas solar-generated electrolysis of water to produce hydrogen and oxygen solar cells as a direct source of electrical energy wind power geothermal power nuclear energy.

Future scenarios predict that there will be no one single replacement fuel. Instead there will be a range of sources of energy, and the use of each will shift as appropriate technology is developed. Different countries have greater or less access to the resources needed, and being able to ensure secure access to the resources is of great economic and political importance. In Chapter 24 we examine some of the possibilities.

2.5

2.0

1.5

1.0

0.5

0.0Mar06

Jun06

Sep06

Dec06

Mar07

Tonn

es

Your greenhouse gas emissions from this account were 1.19966 tonnes

Figure 23.18Household electricity bills may shock the consumer with feedback on the amount greenhouse gas produced as a result of their electricity consumption.

Fossil fuels are derived from the remains of plants and animals that died millions of years ago.

There are large reserves of coal but the reserves of oil and natural gas are limited.

Coal is mainly used in the generation of electricity. Crude oil is a mixture of alkanes. The components in crude oil are separated by fractional

distillation into fractions with similar boiling points.

Heavier fractions can be cracked to produce more of the lighter fractions that are used as petroleum.

Products derived from crude oil include petroleum, LPG, ethene, and other chemicals used in the manufacture of consumer products such as plastics and pharmaceuticals.

Natural gas is used for heating and in electricity generation.

23.123.3summary

1 a The water content of freshly mined brown coal is about 6070%. What implications does this high water content have for the energy released from burning brown coal?

b What pre-treatment could raise the energy content per gram of brown coal consumed in a power station?

c If some electricity produced from burning brown coal was used to reduce its water content, then how could this energy cost be minimised?

d What impact do impurities such as sulfur have on generating electricity from brown coal?

2 In Australia, which resource is likely to last longer before it is depleted, coal, oil or natural gas? Explain your choice.

3 Wood from forests is a renewable resource that supplied global energy needs for thousands of years.a Why is wood no longer sustainable as the major energy

source for todays society?b Is it possible to have a non-renewable and sustainable

energy source? Explain.

c What can be done to increase the sustainability of our planets energy resources? In your opinion, who should make decisions regarding practices that affect sustainability? Discuss your answer with your classmates.

4 Describe two major problems associated with the use of fossil fuels.

5 a Why is it necessary to treat crude oil by fractional distillation?

b What is the function of the bubble caps in the fractionating tower?

c Name three fractions obtained from fractional distillation of crude oil and describe one use for each fraction.

6 a Why is catalytic cracking performed on some of the fractions obtained from crude oil?

b Give an equation that represents the sort of reaction that might take place in a catalytic cracker.

c Name any homologous series that can be produced by this process.

key questions

23

380

key terms

Supplying and using energy

black coalbrown coalbubble capcatalytic crackingenergy converter

feedstocksfossil fuelsfractional distillationfractionsgreenhouse effect

joulenatural gasnon-renewableoilpeat

sustainabilitywaste heat

Coal 7 a A simplifi ed chemical equation for the combustion of coal

can be written as:

C(s) + O2(g) CO2(g)

Sketch an energy profi le for the combustion of coal. Label on your sketch:

i the activation energy ii the energy required to break the bonds in the reactants iii the energy released in forming bonds in the products iv the enthalpy change for the reaction

b Suggest two advantages and two disadvantages of using brown coal to generate electricity.

c Write the equation for the combustion of methane, the main component of natural gas.

d Write the equation for the combustion of hydrogen gas.e Explain which of natural gas, hydrogen or coal will produce

the most (and least) carbon dioxide. 8 The brown coal power stations in Victoria generate a total of

over 30 000 GWh of electrical energy each year. (1 GWh = 3.6 1012 J.)a Calculate how many joules of energy are produced by

these power stations each day.b One tonne of brown coal yields about 8.7 109 J of

energy. On the basis of the current rate of use, calculate how long you expect Victorias estimated 40 000 Mt of brown coal to last. (1 Mt = 106 t.)

c In view of predicted patterns of energy use, would you expect the fi gure calculated in part b to be higher or lower than the actual length of time before brown coal supplies are exhausted? Give reasons for your answer.

d A household uses about 1.7 1010 J in a year. Calculate the mass of coal that is burnt to provide this energy.

9 The Hazelwood power station in the Latrobe Valley consumes about 13 million tonnes of coal in one year. The coal used in the power station is composed of approximately 25% carbon.

Calculate the volume of the greenhouse gas carbon dioxide released each year by the power station. (1 mol of carbon dioxide occupies 24.5 L at 25C and 1 atm; 1 t = 106 g.)

Oil10 Explain why:

a energy from oil is very suitable for transportb electrical energy is very suitable for domestic lighting and

heating11 Crude oil consists mainly of saturated hydrocarbons. a What is meant by the term saturated hydrocarbons? b One of the fi rst steps in processing crude oil is fractional

distillation. What is the purpose of this step? c Some of the fractions obtained from fractional distillation

are subjected to catalytic cracking. What is the purpose of catalytic cracking?

12 Crude oil is a mixture of hydrocarbons including C15

H32

, C3H

8,

C9H

20, C

30H

62 and C

5H

12.

a In what order would these hydrocarbons liquefy as a gaseous mixture moves up the fractionating tower? Explain.

b Copy and complete the table below to show what fraction each of these compounds belongs to and its main uses.

Hydrocarbon Fraction UseC

15H

32

C3H

8

C9H

20

C30

H62

C5H

12

13 The US has 5% of the worlds population, but consumes about 25% of the total oil produced in the world. The nation consumes nearly twice as much oil as it produces.a Account for this high rate of oil usage in the US.b What political and economic problems could result from

this rate of oil consumption?c Do you think that nations such as the US that consume

large amounts of energy have special responsibilities to the rest of the world?

d Suppose that the US government desired to reduce the nations dependence on oil. What steps might be most effective in i the short term? ii the long term?

381381Fossil fuels

14 Dmitri Mendeleev, the Russian chemist who developed the periodic table in 1869, said that burning petroleum would be akin to fi ring up a kitchen stove with banknotes. Why do you think he believed petroleum was too valuable to burn?

Connecting the main ideas15 Use the Internet to fi nd out which nations are the top ten

consumers of energy.16 When natural gas burns, carbon dioxide and steam are

formed. An advertisement for the South Australian Gas Company Limited claimed that, If you use natural gas in your home for cooking, water heating and space heating, youll cut carbon dioxide emissions by up to 60% compared to other forms of energy. Explain why the company could make this claim.

17 Rather than spending money to reduce gas emissions from their power stations further, the Dutch government decided to spend $35 million on reduction of sulfur emissions in nearby Poland and $300 million in tropical countries to plant new trees in areas where trees have been felled. Why might the government have made this decision?

18 The 1997 Kyoto Protocol was an international response to global warming in which the developed nations were asked to restrict their carbon dioxide emissions to set amounts. Australia was asked to restrict its emission of greenhouse gases to 108% of the level in 1990.a Australia has huge reserves of coal. What impact would

adoption of the Kyoto Protocol have on this country?b Suggest why an increase of 108% of emissions, rather

than a decrease, was set as a target for Australia.19 There is an emerging concern that CO

2 emissions could lead

to increasing acidifi cation of our oceans, with consequent impacts upon marine life and, in turn, ours.a What chemical reaction is likely to be the basis of this

concern?b With reference to equilibrium, is such a change and its

effects likely to be permanent?c What is the role of the scientifi c community in checking

such a claim?d If true, how could marine acidifi cation infl uence a choice

between coal, petrol and other forms of energy?e How would the successful development of

geosequestration (capture and burial of emitted CO2)

change your answer to part c?

chapter 24

chapter outcomes

key knowledge

22Alternative

energy sources

comparison of energy sources: types, uses and sustainability, including brown coal, natural gas, nuclear fi ssion and biochemical fuels


describe the range of alternative energy sources available to society, including nuclear fi ssion and fusion and biochemical fuels

identify some advantages and disadvantages in the use of nuclear energy and biochemical fuels

distinguish between renewable and non-renewable energy sources

use social, economic and environmental factors to compare common energy sources

assess the suitability of various energy sources for particular situations

explain how energy conservation and consumption affect the sustainability of energy sources.

24444444424224Alternative energy sources 383

Figure 24.1Projected changes in the worlds consumption of energy.

20000

15000

10000

5000

2000 2010 2020 2030

CoalOil

GasNuclear

HydroOther renewable

Mill

ion

tonn

es o

il eq

uiva

lent

As we saw in Chapter 23, the worlds dependence on fossil fuels poses two main problems: resources are fi nite, so use of fossil fuels is not sustainable burning fossil fuels releases carbon dioxide, leading to global warming

and climate change.Consumption of energy is predicted to increase, both in developed countries and with increasing industrialisation of developing countries such as India and China (Figure 24.1). This means that problems of supply and environmental impact are also predicted to increase unless alternative sources of energy are found. This chapter explores some of the possible alternatives.

24.1

Nuclear energyFission reactorsLarge quantities of energy are released when the nucleus of the uranium isotope 23592U splits in response to being bombarded by neutrons. The nuclei split in a process called nuclear fi ssion. New elements are formed in this process, so it is described as a nuclear reaction. The neutrons produced in this process then split more uranium atoms, so producing more energy and more neutrons. This process continues, causing a chain reaction that yields considerable energy (Figure 24.2).

!Chemical reactions involve rearrangements of atoms. Elements present in the reactants are always present in the products. Nuclear reactions involve rearrangements of protons and neutrons in atomic nuclei to form different elements.

chemfactUranium deposits contain two isotopes, 99.3% uranium-238 and 0.7% uranium-235. The uranium-235 isotope undergoes fi ssion readily. Uranium-238 decays progressively to produce stable lead-206. Fuel for nuclear power stations is enriched so that it contains 2% to 3% uranium-235. Weapons-grade uranium contains about 90% uranium-235.

chemfactUranium-235 is naturally radioactive, with a half-life of 7 million years. This spontaneous decay is a different process from the fi ssion caused by bombardment with neutrons in a nuclear reactor.

Figure 24.2A nuclear fi ssion chain reaction.

23592U

14056Ba

14056Ba

14056Ba

14056Ba

9336Kr

9336Kr

9336Kr

9336Kr

23592U

23592U

23592U

10n

10n

10n

10n

10n

10n

10n

10n

10n

10n

10n

10n

10n

10n

Neutron =


The energy released from the fi ssion of uranium-235 atoms can be used as the heat source for generating electricity in a power station. One kilogram of uranium produces about the same electrical energy as 2500 tonnes of coal. Thermal energy is used to produce steam. The steam drives a turbine connected to an electricity generator, as shown in Figure 24.3.

Over 30 countries, including France, the US, countries from the former USSR, Japan and the UK, are operating a total of more than 440 nuclear power stations. Several other countries are planning and building reactors. Some nations, particularly in Asia, are expanding their nuclear power. In contrast, nuclear plants are closing in parts of western Europe. Some countries are completely dependent on nuclear power for electricity generation. Others, such as Australia, do not use nuclear power stations, although a small research reactor operates at Lucas Heights, near Sydney, producing medically and industrially important isotopes.

Reactor designs vary. In some nuclear reactors, control rods containing neutron absorbers such as boron are inserted between fuel rods containing uranium to control the reaction rate. The reactor vessel is in water, which cools it and also absorbs neutrons to moderate the chain reaction, below.

10n +

23592U

14056Ba +

9336Kr + 3

10n + energy

Other fi ssion reactions for uranium-235 include:10n +

23592U

14456Ba +

9036Kr + 2

10n + energy

10n +

23592U

14156Ba +

9236Kr + 3

10n + energy

10n +

23592U

13052Te +

9440Zr + 3

10n + energy

In these fi ssion reactions a small amount of mass is converted to energy. The amount of energy (E) obained when mass (m) is converted to energy is given by E = mc2, where c is the speed of light.

Most isotopes directly formed from the fi ssion of uranium have atomic masses spread around 95 and 135. Most are radioactive and undergo further decay until stable isotopes are formed. Table 24.1 gives the half-lives of some radioactive products from uranium-fuelled nuclear power stations.

Figure 24.3Elements of a nuclear power station.

Control rods

Reactorvessel

Uraniumfuel

Pump

Concrete containmentbuilding

Pump

Boiler

Steam

Turbine

Condenser

To cooling towers

Circulating reactorcoolant

Electricity

Generator

Radioactive isotope Half-lifeRadon-222 3.8 daysIodine-131 8 daysKrypton-85 10 yearsHydrogen-3 (tritium) 12 yearsStrontium-90 29 yearsCaesium-137 30 yearsAmericium-241 443 yearsRadium-226 1622 yearsPlutonium-239 24 000 yearsThorium-230 80 000 years

TABLE 24.1 Half-lives of some radioactive isotopes produced by nuclear power stations


Nuclear waste

The presence of radioactive isotopes in spent fuel obviously demands long-term waste disposal solutions. A typical nuclear power station might produce 30 tonnes of spent fuel each year. Some of this spent fuel is uranium and plutonium that can be recycled, but there is also about 1 tonne of unwanted, highly radioactive material produced each year. This material can be solid, liquid or gaseous, depending upon the design of the particular reactor from which it comes.

Steel and concrete containers are used to transport nuclear waste by road and rail.

As a consequence of its radioactivity, nuclear waste gives off a considerable amount of heat and must be stored for about fi ve years to allow short-lived radioactive isotopes to decay and the material to cool down (Figure 24.4). The waste containing the longer-lived isotopes must then be stored safely for several thousand future generations. (The Great Pyramid of Egypt was built only around 200 generations ago!)

Methods used to store waste include: burial in sealed tanks or stockpiling in deep mines in geologically stable

regions stockpiling in air-conditioned warehouses dumping sealed containers of waste in deep ocean trenches sealing it in a special type of glass.

Fission is not the only source of troublesome radioactive by-products. Instead of undergoing fi ssion, uranium-238 in the fuel rods can sometimes capture a neutron generated by the fi ssion of uranium-235 to form plutonium. This reaction is exploited in breeder reactors. Plutonium is used in some power stations and in nuclear weapons, but as a component of nuclear waste it is particularly troubling as it has a half-life of 24 000 years.

23892U +

10n

23992U

23992U

23993Np +

01e

23993Np

23994Pu +

01e

Figure 24.4Where should we put all the nuclear waste? This spent fuel is stored in a ventilated vault at the Wylfa nuclear power station in Wales.

chemfactA ceramic called Synroc was used to trap plutonium waste stockpiled in the United States during the Cold War. Synroc is made from several natural minerals and is able to incorporate into its crystal structure nearly all of the elements found in high-level radioactive waste. It is claimed to be the most effective and durable material for immobilising various high-level radioactive wastes for disposal, and was developed in 1978 by Professor Ted Ringwood at the Australian National University.

Figure 24.5These storage tanks in Washington State in the US store high-level liquid waste. The tanks were buried in earth after construction.


Advantages and disadvantages of nuclear power

A hazard associated with nuclear power is the release of radioactive substances by accident, hijacking or sabotage. Major accidents at Three Mile Island in the US in 1979 and Chernobyl in the former USSR in 1986 both released radioactive particles in dangerous amounts (Figure 24.6). On the positive side, accident rates are very low in nuclear power plants.

There is also concern that radioactive material designed for peaceful uses could be diverted and used in the manufacture of weapons.

In contrast to fossil-fuel power stations, nuclear power stations are not usually sources of air pollution. Nuclear power stations offer us the chance to conserve fossil fuels, and consequently reduce acid rain and the production of greenhouse gases. They also have some drawbacks, including a long construction time, often about a decade or more from planning to commission, and a limited working life before they need to be decommissioned. Greenhouse gases are produced in the mining, transport and refi ning of uranium and in the construction of nuclear power stations. There is also low-level nuclear waste produced in mining uranium ore, and in by-products from refi ning the ore.

In summary, the greatest problems associated with nuclear energy are: the disposal of highly radioactive waste materials, many with long half-

lives and the potential to enter the food chain the risk and consequences of serious accidents or terrorist attacks

involving nuclear reactors.

Figure 24.6The nuclear power station at Chernobyl. Some scientists predicted that thousands of people would die of cancer from radiation released during the accident, an estimate confi rmed by Greenpeace International in 2006.

US backs Australias uranium plan

The United States has backed a plan by Australia to sell uranium to China for nuclear power as long as there are strict safeguards to stop it falling into the hands of terrorists.

US Energy Secretary Sam Bodman . . . said countries around the globe were facing an increase of about 50 per cent in demand for electricity in the next 20 years and would have to look at developing nuclear power in response.

While Australia remains cagey about whether it will adopt nuclear power, Mr Bodman said the US had no problem with the federal government selling uranium to China.

We dont object to that, Mr Bodman told reporters.

However we would encourage both the Australians as well as the Chinese to make sure there are adequate safeguards in place there is concern over the potential access of terrorists to nuclear material.

Australias Industry Minister Ian Macfarlane said Australia was yet to have a proper debate based on facts rather than emotion about adopting nuclear power in Australia.

Whether or not Australia goes down that [nuclear] path or looks at a different mix of renewable energy along with zero emission coal it really needs to be debated.

Source: AAP, in the Age, 11 January 2006

Nuclear trade

extension

E1 Australia and China are both signatories to the Treaty for the Non Proliferation of Nuclear Weapons. Use the Internet to fi nd out about the purposes of this treaty.

E2 Identify some of the issues involved in the mining of uranium and its sale to other countries.

questions ?


Advocates for nuclear power argue that: environmental damage associated with nuclear reactors is less than that

caused by the burning of fossil fuels costs and supply of imported oil have been unreliable while nuclear

energy is readily available another energy form is required to replace diminishing fossil-fuel

reserves switching to nuclear power stations will reduce greenhouse gas emissions

and global warming.The worlds reserves of uranium are estimated at 1 1015 MJ, suffi cient for more than 100 years at current consumption rates. Australia has between one quarter to one third of the worlds known reserves of uranium ore, U3O8. Some of Australias uranium is exported, although there is vigorous debate about whether it should be mined and sold.

Nuclear fusionAt extremely high temperatures, hydrogen nuclei can combine to form helium nuclei, with no radioactive by-products. Such a process, in which a larger nucleus is formed from smaller ones, is called nuclear fusion. Nuclear fusion occurs in the Sun and is the source of solar energy. The step-wise nuclear reaction can be summarised as:

411H 42He + 2

01e + energy

Nuclear fusion also occurs when a hydrogen bomb is detonated, but such a rapid release of energy is unsuitable for a power station. Controlled nuclear fusion, if it were possible, would offer clean and safe power. One kilogram of fusionable material may yield the energy available from 10 000 000 kg of fossil fuel.

Two main problems have been encountered in the development of this energy source: sustaining the temperatures of 100 000 000C required for the reaction containing material at such high temperatures. Recent experiments

involve the use of containers made from magnetic fi elds.There is a prospect of nuclear fusion becoming a useful energy source at some future date. France, in partnership with the European Union, Japan, Russia, India, South Korea, China and the United States, has recently announced the proposed construction of a nuclear fusion demonstration power plant at Cadarache, near Marseille. This quest for controllable fusion has immeasurable rewards for us all if it can be achieved.

!01e represents a positrona small, positively charged particle the size of an electron.

During nuclear reactions, protons and neutrons in the nuclei of atoms are rearranged to form new elements.

In a fi ssion reaction the nucleus of a heavy element is split, forming the nuclei of lighter elements.

In a fusion reaction the nuclei of lighter elements combine to form the nucleus of a heavier element.

23592U is used as the fuel in a nuclear reactor.

The generation of electricity using nuclear power does not produce CO

2, a greenhouse gas.

There are large reserves of uranium readily available in Australia.

The wastes from nuclear power stations remain radioactive for a long time, posing a problem for their long-term storage and disposal.

There is community concern about the risk of accidents involving nuclear power stations.

Radioactive waste contains materials that can be used to manufacture nuclear weapons.

24.1summary


1 Australia exports most of the uranium it mines rather than using it for domestic nuclear power stations. Respond to each of the following questions, giving the reasons for your response in point form.

a Should Australia take back the waste products from nuclear power stations fuelled by Australian uranium?

b What possible changes might lead to a greater use of nuclear power in Australia?

key question

24.2

Renewable energy sourcesRenewable energy sources are those that are continually being replaced by natural processes. These sources include rivers, tides, waves, rubbish tips, plant crops, hot underground water, and the Sun.

Some of the most exciting recent developments in science are in the area of renewable energy sources. Rapid technological advances mean that many alternative energy sources viewed as exotic or fanciful a decade or two ago are now economically viable.

Biochemical fuelsThe use of crops such as sugar to produce ethanol for use as a petrol additive and canola to produce biodiesel was discussed in Chapter 11. These are considered to be a renewable energy source as natural processes, the growth of plants, can be used to produce them. They are also considered by some to be carbon dioxide neutral in that carbon dioxide is consumed in the photosynthesis reaction that occurs in plants.

You will recall that ethanol for use as a fuel can be produced by the fermentation of glucose:

C6H12O6(aq) enzymes 2CH3CH2OH(aq) + 2CO2(g)

Research into the conversion of cellulose and other fi brous plant wastes into ethanol may result in an increase in the amount of ethanol produced from plant material. Blends of 10% ethanol with petrol, known as E10, can be used in petrol engines.

Biodiesel is derived from vegetable oils and animal fats that are hydrolysed to produce fatty acids which in turn are reacted with methanol to produce the esters that make up biodiesel:

CH3(CH2)14COOH(l) + CH3OH(l) CH3(CH2)14COOCH3 + H2O(l) Fatty acid Ester (biodiesel)

Waste plant material can be converted into the mixture of carbon monoxide and hydrogen known as syngas, which can be used to generate heat and electricity. It can also be converted into diesel.

Animal waste and plant material can also be used as a source of biogas, by using a biogas digestor, as described in Chapter 11. Biogas is a popular form of energy in many developing countries where people rely on burning biomass, wood, stubble or animal dung for their cooking and heating needs.

!You can fi nd out more about Australias non-renewable and renewable energy resources by following the link from hi.com.au.


chemistry in action

Hydrogen: a fuel of the future?

Hydrogen gas can be produced simply from the electrolysis of water, using a range of renewable or non-renewable energy sources to drive the process. A future means of production that is still in the laboratory developmental stage is to obtain hydrogen from the green chloroplasts in spinach using an enzyme from the bacterium Escherichia coli. Other lines of research involve the use of different bacteria and also using light to reduce carbon dioxide to the methanoate ion, HCOO, followed by the use of enzymes to convert this to hydrogen and carbon dioxide. Research is also under way into electrolysis by photobiological methods whereby microbes exposed to sunlight split water to produce hydrogen and oxygen, and photoelectrolysis by photoelectric semiconductors placed in water. The overall reaction is:

2H2O 2H2(g) + O2(g); H = 571 kJ mol1

This reaction is reversed when hydrogen is burnt, say in a motor vehicle, releasing 142 kJ per gram of hydrogen consumed.

About 95% of the hydrogen produced today is extracted from methane using high-temperature steam (steam methane reforming, see Chapter 19) in a two-step sequence:

CH4(g) + H2O(g) CO(g) + 3H2(g)CO(g) + H2O(g) CO2(g) + H2(g)

Hydrogen is a contender for the top motor fuel in the next few decades (Figure 24.8). All major car manufacturers are developing engines that are able to use hydrogen as a fuel. The big advantage of hydrogen is its non-polluting combustion, although greenhouse gases are released if coal or other fossil fuels are used to produce the hydrogen in the fi rst place. It is an extremely light and highly fl ammable gas, and problems remain with its safe use and setting up a distribution infrastructure.

Hydrogens low energy density at standard temperature and pressure make it diffi cult to store in a small fuel tank. One of the most promising developments is in improved storage technology in hydrogen-powered motor vehicles, giving them a range comparable to that of petrol-powered cars.

Figure 24.8A hydrogen fuel-cell vehicle fi lls up at the fi rst retail hydrogen dispenser in the US. Major car manufacturers expect to have hydrogen vehicles in mass production by 2010.

Figure 24.7Hydrogen production in the future.

Photovoltaic power

Wind power

Hydroelectricity

Solar thermal electricity:the collectors concentrate

the sunlight to heat oil,which is used to generate

steam to drive turbines

d.c. electricity

a.c. electricity

Water

Electrolyser

Compressor

Pipelineto user

Compressedhydrogen gas

Hydrogen gas

Oxygen gasRectifier

!The E. coli bacterium is not usually such a helpful organism. It is commonly found in raw sewage and can cause food poisoning. However, it has been well studied for many years and is often used as a basis for genetic engineering.


Solar energyThe energy in fossil fuels, and most of the other forms of energy that are described in this chapter, originate from energy supplied by the Sun. Solar energy can also be used directly.

The Sun provides the Earth with about 1020 J of energy per hour.Solar-effi cient design of buildings dramatically reduces heating, cooling

and lighting costs. Solar water-heating systems can provide hot water for domestic or industrial purposes such as heating homes, water for domestic use and for use in swimming pools.

chemistry in action

Hydrogen: a fuel of the future? (continued)

Fuel cells, which are described in Chapter 27, convert chemical energy into electrical energy. They offer the promise of clean and safe energy. Heat and water are the only waste products from hydrogenoxygen fuel cells. Fuel cells can be up to 80 per cent effi cient. At this rate, they can produce electricity much more effi ciently than it can be produced by fuel combustion in a conventional power station.

Fuel cells in hydrogen-powered vehicles are currently more expensive and short-lived than other fossil-fuelled engines, but fuel cells have been used successfully in the United States Space Shuttle. Ongoing technological improvements are paving the way for the large-scale commercial use of fuel cells.

Wide eavesto protectwindows fromsummer sun

Summer sun

Solar water heater

Winter sun Insulation to preventloss of heat in winter

Large windows toadmit winter sun

Solid building materialsto store heat

Figure 24.9Features of a solar-effi cient house.

Figure 24.11This solar-powered aircraft has a 63 m wingspan. It is designed to carry scientifi c instruments to heights of up to 30 000 m.

Filter

Pump

Solarcollector

Hotwater

Coldwater

Figure 24.10A solar pool heater. Solar water-heating can provide more than 60 per cent of the energy required to heat a swimming pool.


Electricity can also be generated by using parabolic collectors or dishes to focus the Suns energy (Figure 24.12). A liquid is used to transfer the heat from this point to a turbine and generator, as in a coal-fi red power station.

The disadvantages of generating electricity using solar cells are that: they are expensive they are less effective in cloudy weather and do not operate at night large areas of land are needed for collection because of their relatively

low effi ciency as energy converters.

Hydroelectricity: a solar-powered water wheelHydroelectricity is obtained by using the energy of falling water to drive turbines connected to electricity generators. In a sense, hydroelectric power stations are solar powered. Solar energy evaporates water, transferring it from low to higher altitudes in the form of rain. Gravitational potential energy is converted to kinetic energy as rainwater in rivers fl ows downhill (Figure 24.13).

Hydroelectric power stations supply about 25% of the worlds and 10% of Australias electricity. Further development of this energy resource is possible in Australia, but will be restricted because of: a limited number of suitable sites concerns about the environmental impact of building large dams.

To dam or not to dam? In order to provide a reliable fl ow of water in all seasons of the year it is often necessary to build a storage dam in a river. Land must be fl ooded in order to build a dam and environmental issues associated with the fl ooding of land are frequently diffi cult to resolve.

Wind powerWindmillswind operated water pumpsare iconic features of the Australian outback. Wind-powered electricity generators are a more recent development. They are usually sited near the coast to take advantage of higher wind speeds. Average wind speeds exceeding 5 m s1 are regarded as suitable for electricity generation. Wind-powered generators have been used successfully to supply electricity to towns in Europe and the United States (Figure 24.14), and a 14-turbine wind farm is planned for the south-western coast of Victoria. Other wind turbines are appearing elsewhere in Victoria.

City Average solar energy levels (MJ m2)

Adelaide 18.0Brisbane 17.9Canberra 17.5Darwin 21.3Hobart 13.8Melbourne 14.7Mildura 18.6Sydney 16.4Perth 18.9

TABLE 24.2 Average daily solar energy received for some Australian cities

Figure 24.12Rows of dishes form part of a solar power station serving the remote township of White Cliffs in New South Wales.

Figure 24.13The operation of a hydroelectric power station.

Dam

Dam wall

Pipeline

Turbine andgenerator

!It has been estimated that there is suffi cient roof space on Australian homes to meet Australias current electrical energy needs using photovoltaic cells. Less than 1% of Australias energy needs are currently met by solar energy.


The disadvantages of wind-powered electricity generation are that: the turbines are highly visible and their effect on the landscape must be

considered the moving blades of the turbines produce some noise so they must be

sited away from populous areas electricity production is dependent on wind speeds and is no more

reliable than the wind very large numbers of turbines are needed to equal the output of a coal-

fi red power station.The siting of wind farms is often a contentious issue. The construction of a wind farm was blocked by a federal minister in 2006 on the basis of threats to the endangered Orange-bellied Parrot, a bird with indeterminate fl ightpaths that had been reported in the area of the proposed wind farm. The decision was reversed later that year when revised plans were prepared locating the wind farm a little further from the coast. Despite these problems, wind power is a promising and non-polluting way of harnessing a free form of energy.

Tidal power: power from the Moon

Figure 24.14Wind turbines dot the landscape.

Figure 24.15A power station at La Rance, France, produces electricity from tides.


A Melbourne company is installing wave-power generation units in the ocean near Portland. The power generated will be sold to electricity companies. Each generator produces about 20 kilowatts of electricity, which is suffi cient to power about 10 to 20 houses. Average wave heights of 2.5 metres off the Australian coast are ideal for wave-energy production. A tidal power station at La Rance in France generates up to 240 megawatts of electricity by capturing the incoming tide in sluice gates and then releasing the water via turbines (Figure 24.15).

Tidal power stations are best located where there is a large drop between high and low tides. There are several potential sites in Australia, particularly in north-west Western Australia, where the difference between high and low tides can be as much as 11 metres.

Geothermal powerIn volcanic regions of the world, heat fl owing from hot underground rocks to underground water may cause superheated steam to reach the surface. The energy from the steam can be harnessed to produce electricity. Geothermal power stations have been built in New Zealand and at other locations. This is a proven, cheap and relatively clean form of power. Like tidal power, geothermal power generation is restricted to suitable sites.

Away from the more active volcanic areas, underground water at temperatures of 30 to 80C can be used to heat buildings, domestic water and for industrial processes. The city of Portland in Victoria is located near a volcanic hotspot. There, hot water from a well is used to heat a swimming pool and six major buildings, reducing the citys annual fuel bill by several hundred thousand dollars.

Conservation: the hidden energy sourceYou will appreciate by now that choosing energy sources for the future is a complex process that requires us to weigh up the advantages and disadvantages of each source.

There are two main ways in which we can extend the lives of our non-renewable energy reserves: develop alternative energy sources to produce more energy conserve our existing energy reserves by using less energy.

The government has encouraged and demanded energy conservation through rebates for householders who install solar heating and solar panels, and legislation to enforce new building codes for energy-effi cient housing.

You can practise some energy conservation measures as an individual; others require people to cooperate and work as a group. Some measures, such as turning off the television instead using the standby feature, will barely affect your lifestyle; others are more drastic. The selection and use of the best energy sources requires us to make decisions. The decisions that we make as individuals and those made by our governments will determine the quality of our lives in the future.

394

key terms

Supplying and using energySupplying and using energy

394

The page A header goes here


394

the cutting edge

One of the reasons solar energy has attracted so much interest is that the Sun provides the Earth with more energy per hour (4.3 1020 J) than all the energy consumed by the planet in a year (4.1 1020 J). However, converting even a small fraction of this into useable electricity remains challenging, both scientifi cally and technically. Current solar panels are made of crystalline silicon, which have practical effi ciencies of about 12%. They are very expensive to produce as their manufacture often requires high-temperature and high-vacuum techniques. By making sandwich-like devices from silicon, cadmium, telluride, indium, gallium and arsenic, people have been able to generate higher effi ciencies (30%); however the costs of such devices are prohibitive ($US50 000 per square metre) and many of the components are toxic.

We are developing a new generation of electroactive polymers that will allow us to make large-area, low-cost solar panels that have effi ciencies greater than 10% (Figure 24.16).

Converting solar energy into electricity involves the following steps:1 absorbing as much light as possible

across the solar spectrum, from the ultraviolet through to the infrared

2 transferring that energy to a reactive site in the device

3 using the energy to generate charges (i.e. move an electron from one molecule to another, thereby creating positive and negative moleculesa so-called exciton)

4 separating these charges in space before they can recombine

5 moving these charges to separate electrodes

and fi nally6 moving the charge through an external

circuit.The overall solar cell effi ciency depends

on the effi ciencies of each of these steps.Polymers are best known as insulators;

however in the late 1980s Heeger, McDiarmid and Shirakawa discovered that some polymers could become conductingand for this work they received the 2000 Nobel Prize in Chemistry. So in principle we now have molecular wires along which we can move electrical charge.

Over the past decade we have developed techniques that give precise control over both the polymer chain length and the polymer architecturethe sequence of monomers in a copolymer. We have made controlled polymer structures composed of various dye molecules that: absorb in different parts of the solar

spectrum transfer this energy with high effi ciency

(> 95%) to a reaction site produce an exciton, again with high

effi ciency (Figure 24.18).We are now integrating these polymers

with conducting polymers of the type shown in Figure 24.17 and with other additives such as C

60 (a hollow ball of carbon atoms)

to make prototype solar cells. The aim is to develop a low-cost, roll-to-roll printing technique to produce large-area solar cells that have high effi ciencies.

by Gerry Wilson

Figure 24.16Construction of a typical organic photovoltaic device. The active layer (red) can be a bilayer of vapor-deposited molecules, or an interpenetrating network of polymers with C

60

or an inorganic quantum structure.

Polymer solar cells

bioo

Alternative energy sources

395

Dr Gerry WilsonDr Gerry Wilson received his PhD from the Australian National University and an undergraduate degree in Chemistry from University College, Dublin. Following research fellowships at the universities of New South Wales and Melbourne, he joined CSIRO to work on security features for high-security documents. His inventions appear on several currencies around the world.

n

O

O

OOMe

()

Figure 24.17A typical conjugated polymer (MDMO-PPV) and a soluble derivative of C

60 (PCBM) used in an all-polymer

solar cell.

Figure 24.18Construction and performance of a star shaped, light-harvesting polymer having 24 coumarin monomers (in blue) and 36 acenaphthalene monomers (in green) per arm. The reaction site is the core of the molecule, which is based on a ruthenium bipyridine complex (in yellow). The solid black arrow indicates the direction of energy transfer and the red arrow indicates electron transfer from the ruthenium core to a methyl viologen molecule (in red).

Figure 24.19Gerry Wilson at work in his laboratory.


Source Advantages DisadvantagesCoal Large Australian reserves Non-renewable

Easily mined Causes greater pollution than oil and natural gas

Low cost

Provides export income

Oil Limited Australian reserves Non-renewableEasily transported Limited world supplies

Many uses Causes pollution

Natural gas Limited Australian reserves Non-renewableEffi cient source of domestic heat Causes pollution, although less than coal and oil

Moderate cost

Nuclear fi ssion Large Australian reserves Non-renewableHigh energy output per unit mass of fuel Radioactive waste disposal, long half-life of nuclear wastes

Low accident rate Accidents have great impact

Provides export income Security risks

Nuclear fusion Large global fuel reserves Unproven high-cost technologyHigh energy output per unit mass of fuel Radioactive waste disposal

Solar Renewable

Low running costs

Effi cient heating

Causes little pollution

Dependent on weather

Large collectors needed

Hydroelectricity Renewable


Low running costs

Restricted sites

Dam destroys local habitat

Wind Renewable


Low running costs

Dependent on weather

Restricted sites

Tidal/wave Renewable


Dependent on tides/waves

Restricted sitesBiomass (wood, biogas, ethanol, biodiesel)

Low running costs

Renewable

Biogas uses wastes

Low CO2 emission per unit mass of fuel

Production via photosynthesis absorbs CO2

Limited rate of supply

Low energy output per unit mass of fuel

Hydrogen gas Non-polluting emissions

Produced from water using electricity

Low energy density for storage

New distribution infrastructure required

Co-development of fuel cell technology required

TABLE 24.3 Some advantages and disadvantages of energy sources available in Australia

24.3

A time for decisions


How do we choose what energy sources to use? How much, how quickly, for which purpose and in what ways should we use energy? What are the risks and how can we manage them? What will future demands be? These are not easy questions to answer. To reach a decision we must carefully balance the benefi ts and costs (and risks) of each option. The advantages and disadvantages. of various energy options are summarised in Table 24.3.

The lives of non-renewable energy resources can be extended by conserving existing reserves and by developing alternative energy sources.

Renewable energy resources are continuously being replaced by natural processes.

Biochemical fuels such as ethanol, biodiesel and biogas are produced from plant materials.

Other renewable sources of energy include solar, wind, hydro, geothermal and tidal power.

24.224.3summary

2 Bagasse, the fi brous waste from sugarcane mills, is burnt to satisfy about 2% of Australias energy needs. Firewood satisfi es a similar amount. Should we use more or less of these renewable resources? Justify your answer.

3 a Select a form of biochemical energy and one other form of renewable energy. For your chosen energy sources:

i draw up a table that summarises their advantages and disadvantages

ii comment on their usefulness in supplying the future energy needs of your local community.

b Repeat part a for two non-renewable forms of energy.

key questions

24

398

key terms


biogaschain reactiongeothermal power

hydroelectricitynuclear fi ssionnuclear fusion

renewablesolar energytidal power

wind power

Nuclear energy 4 a Write an overall equation for the formation of plutonium-

239 from a neutron hitting uranium-238 in a nuclear reactor. Hint: use electrons (beta particles, 1

0) in your equation.

b Plutonium can be used to make atomic weapons. What implications does this have for global security when a nation decides to introduce nuclear power? Suggest some safeguards to minimise nuclear proliferation.

5 Research the characteristics of some radioactive isotopes in spent nuclear fuel that make them particularly hazardous to human health.

6 Australia has large reserves of uranium. At present, it has no nuclear power stations and exports only a limited amount of this source of energy. Discuss with other members of your class the benefi ts and costs associated with the following proposals:a that Australia should build nuclear power stationsb that mining of uranium should be banned

7 The coal versus nuclear power debate has undergone a recent revival in Australia.a Given the choice, would you prefer to live near a coal-fi red

power station or a nuclear power station? Why?b Is there just a choice between coal and nuclear power as

they now operate? What other options exist?

Renewable energy sources 8 Oil, coal and natural gas are described as non-renewable

sources of energy. List three examples of renewable sources of energy.

9 The use of solar energy in Australia is increasing. About 6% of dwellings have solar water-heaters, and around 30 000 new solar water-heaters are being produced each year.a What situations are most suited to the use of solar water-

heaters?b Why do you think that the use of solar water-heaters is not

more widespread?c Solar cars can be constructed and they are cheap to run.

Why then do most people prefer petrol-driven cars?

Energy conservation10 a Summarise the energy that you are supplied with from

outside sources in a single day. Identify the energy source (e.g. coal, gas, etc.) and its application (e.g. transport, hot water, etc.) in your answer.

b How could you change your days activities so that your energy use is minimised? Can you make a difference?

11 The ever-increasing use of computer-controlled systems offers opportunities for increasing our societys effi ciency in using energy. Describe how energy can be saved by the computer control of:a engines in carsb traffi c systemsc household lights and heatingd industrial production systems

Connecting the main ideas12 Changes in energy consumption over time are shown in

Figure 23.3 (p. 368).a In which decade was nuclear energy introduced? What

events led to the introduction of this form of energy?b Why has wood not shown the same increase in

consumption as other fuels?c Suggest why the rate of use of coal was outstripped by the

rate of use of oil.d Describe four ways in which the use of energy in the daily

life of a person living in an Australian city in 1860 would have differed from that of a person living now.

13 Tasmania obtains nearly all of its power supplies from hydroelectricity, whereas Victoria obtains over three-quarters of its electricity from brown coal. Account for the difference between the two states in methods of energy production.

14 Most forms of energy available to us originated from energy supplied by the Sun.a Justify this statement by explaining the origins of wind

energy, oil and hydroelectricity.b List the energy transformations involved in generating

electricity from biogas.

399399Alternative energy sources

15 The Yallourn power station in Victoria has a maximum capacity of 1450 MW. The average daily rate at which Melbourne receives solar energy is 1.0 kW m2.a What area of solar cells, operating at 20% effi ciency,

would produce the same amount of power as the Yallourn station?

b If a typical residential block of land in the city has an area of 750 m2, how many of these blocks does your answer in part a represent?

16 Is there an energy source that may be used without any environmental impact? Explain your answer.

17 Describe how you expect energy to be provided in the year 2050 for each of the following purposes. Give reasons for your answers.a domestic hot waterb domestic lightingc private transportd industrial heating

18 Compare the diagrams showing the operation of a coal-fi red power station (Figure 23.9), nuclear power station (Figure 24.3) and hydroelectric power station (Figure 24.13).a In what ways are the power stations similar?b How do they differ?c Name an advantage and a disadvantage of each form of

energy production.19 Coal, oil, nuclear energy and solar energy are all important

sources of energy today. Give your opinion of the likely importance of each source of energy in:a 10 years timeb 100 years timec 1000 years time

chapter 25

chapter outcomes

key knowledge

22Energy from chemical reactions

application of calorimetry to measure energy changes in chemical reactions in solution calorimetry and bomb calorimetry


write and interpret thermochemical equations perform calculations involving thermochemical

equations compare the specifi c heat capacity of common

materials perform calculations involving specifi c heat

capacities describe the procedure for the electrical calibration

of a calorimeter and calculate a calibration factor from experimental data

explain how solution and bomb calorimetry can be used to determine energy changes of reactions

use calorimetry data to calculate H and heat of combustion for reactions

discuss factors that may affect the selection of a particular fuel for an application.

25555552522Energy from chemical reactions 401

chemistry in action

Explosives: a blast of chemical energy

The Chinese were the fi rst to mix saltpetre, sulfur and charcoal together in AD 919. They quickly realised that there were many uses for this mixture, which later became known as gunpowder. It was put to military use and eventually led to the development of the bombs, cannons and guns which humanity uses so effectively against itself. Today, explosives are an essential tool for mining and other engineering works, such as road construction, tunnelling and building (Figure 25.1). Whereas early mining operations involved thousands of labourers, modern explosives allow millions of tonnes of ore to be set free with a single blast. All along our highways we can see where cuts have been made in the landscape to make way for the road; these cuts have also been created using small quantities of explosives.

Explosives are compounds that transform chemical energy into large quantities of thermal energy. Thermal energy is also released when fuels such as petrol and natural gas burn, but the rate of combustion in such reactions is limited by the availability of oxygen gas to the fuel. The compounds making up an explosive, on the other hand, contain suffi cient oxygen for complete, or almost complete, reaction to occur.

Documents

VCE Chemistry Unit 4