CHEMISTRY OF THE AIR KNOCKHARDY PUBLISHING 2008 SPECIFICATIONS

CHEMISTRYCHEMISTRY

OF THE AIROF THE AIR

KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING2008 2008

SPECIFICATIONSSPECIFICATIONS

INTRODUCTION

This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards.

Individual students may use the material at home for revision purposes or it may be used for classroom teaching with an interactive white board.

Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at...

www.knockhardy.org.uk/sci.htm

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KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING

CHEMISTRY OF THE AIRCHEMISTRY OF THE AIR

CONTENTS• Greenhouse gases

• Greenhouse effect

• Ozone layer

• Pollutants

• Catalytic converters

CHEMISTRY OF THE AIRCHEMISTRY OF THE AIR

GREENHOUSE GASESGREENHOUSE GASES

CARBON DIOXIDE CO2 contains C = O bonds

WATER VAPOUR H2O contains O - H bonds

METHANE CH4 contains C - H bonds

The ‘Greenhouse Effect’ of a given gas is dependent on its...

• atmospheric concentration

• ability to absorb infrared radiation


Different covalent bonds have different strengths due to the masses of different atoms at either end of the bond. As a result, they vibrate at different frequencies (imagine two balls on either end of a spring) . The frequency of vibration can be found by detecting when the molecules absorb electro-magnetic radiation.



Various types of vibration are possible. Bending and stretching are two examples and are found in water molecules. Each occurs at a different frequency.



Various types of vibration are possible. Bending and stretching are two examples and are found in water molecules. Each occurs at a different frequency.

Symmetric Bending Asymmetricstretching stretching



Various types of vibration are possible. Carbon dioxide also undergoes bending and stretching.

Bending in a carbon dioxide molecule


The frequencies lie in the INFRA REDINFRA RED part of the electromagnetic spectrum and can be detected using infra red spectroscopy.

An infra red spectrum of atmospheric air

It is the absorption of infra red radiation by atmospheric gases such as methane, carbon dioxide and water vapour that contributes to global warming.

H2O

H2OCO2

CO2

THE GREENHOUSE EFFECTTHE GREENHOUSE EFFECT

energy from the sun is in the ultra violet, visible and infra red regions



47% reaches the earth



radiation re-emitted from the earth is in the infra red region





70% of the radiation returns to space







greenhouse gasesabsorb the remainder







energy is returned to earth to keep it warm







energy is returned to earth to keep it warm


SummarySummary

• energy from the sun is in the ultra violet, visible and infra red regions

• the earth is warmed up by the energy

• radiation re-emitted from the earth is in the infra red region

• 70% of the radiation (between 7000nm and 12500nm) returns to space

• greenhouse gases absorb the remainder

Gas wavelength of radiation adsorbed / nmCO2 12500 - 17000H2O 4500 - 7000 and above 17000

• they can return this energy to earth to keep it warm


ProblemsAn increase in the concentration of greenhouse gases leads to climate change / global warming.



PossibleEffects



PossibleEffects • higher temperatures

• melting ice caps

• rise in sea levels

• flooding of low-lying lands

• changes in crop patterns

• deserts move north

• change in food webs

• extinction of some species


What can chemists do to minimise climate change from global warming?

• provide scientific evidence to governments to confirm it is taking place

• monitor progress against initiatives such as the Kyoto protocol

• investigate solutions to environmental problems


What can chemists do to minimise climate change from global warming?

• provide scientific evidence to governments to confirm it is taking place

• monitor progress against initiatives such as the Kyoto protocol

• investigate solutions to environmental problems

plus

CARBON CAPTURE AND STORAGE (CCS)

• removal of waste carbon dioxide as a liquid injected deep in the oceans

• storage underground in deep geological formations

• reaction with metal oxides to form stable carbonate minerals.

MgO(g) + CO2(g) —> MgCO3(s)

or CaO(g) + CO2(g) —> CaCO3(s)

CCARBON DOXIDE ARBON DOXIDE CCAPTURE & APTURE & SSTORAGETORAGE


What is it?

• CO2 is collected from industrial processes and power generation

• it is separated and purified

• it is then transported to a suitable long-term storage site


What is it?




Storage possibilities

• gaseous storage in deep geological formations

• liquid storage in the ocean

• solid storage by reaction as stable carbonates


What is it?








How can it help?

• could reduce CO2 emissions from power stations by 80%

• could be used to store CO2 emitted from fermentation processes


What is it?








How can it help?

• could reduce CO2 emissions from power stations by 80%

• could be used to store CO2 emitted from fermentation processes


CO2 in geological structures is actually a naturally occurring phenomenon

• CO2 is pumped deep underground

• it is compressed by the higher pressures

• it becomes a liquid, which is trapped between the grains of rock

• impermeable rock prevents the CO2 rising back to the surface • drilling for CO2 can be used for enhanced oil or gas recovery

Over time CO2 can react with the minerals in the rock, forming new minerals and providing increased storage security.

DEPLETION OF THE OZONE LAYERDEPLETION OF THE OZONE LAYER

Although ozone is a reactive and poisonous gas, it protects us from harmful UV radiation which would affect life on earth. UV radiation can cause skin cancer.



Ozone in the stratosphere 2O3 —> 3O2

breaks down naturally

Ozone (trioxygen) can break up O3 —> O• + O2

to give ordinary oxygen and anoxygen radical



Ozone in the stratosphere 2O3 —> 3O2

breaks down naturally

Ozone (trioxygen) can break up O3 —> O• + O2

to give ordinary oxygen and anoxygen radical

Ultra violet light can supply the energy for the process. That is why the ozone layer is important as it protects us from the harmful rays.

BUTbreakdown is easier in the presence of chlorofluorocarbons (CFC's)


EFFECT OF CFC’SEFFECT OF CFC’S

There is a series of complex reactions but the basic process is :-

CFC's break down in the presence CCl2F2 —> Cl• + CClF2

of UV light to form chlorine radicals

chlorine radicals react with ozone O3 + Cl• —> ClO• + O2

chlorine radicals are regenerated ClO• + O —> O2 + Cl•

Overall chlorine radicals are not used up so a small amount of CFC's can destroy thousands of ozone molecules before the termination stage.


OXIDES OF NITROGEN NOxOXIDES OF NITROGEN NOx

Oxides of nitrogen, NOx, formed during thunderstorms or by aircraft break down to give NO (nitrogen monoxide) which also catalyses the breakdown of ozone.

nitrogen monoxide reacts with ozone O3 + NO —> NO2 + O2

nitrogen monoxide is regenerated NO2 + O —> O2 + NO

POLLUTANTSPOLLUTANTS

POLLUTANT GASES FROM INTERNAL COMBUSTION ENGINESPOLLUTANT GASES FROM INTERNAL COMBUSTION ENGINES

Carbon monoxide CO

Origin • incomplete combustion of hydrocarbons in petrolbecause not enough oxygen was present

Effect • poisonous • combines with haemoglobin in blood • prevents oxygen being carried to cells

Process C8H18(g) + 8½O2(g) —> 8CO(g) + 9H2O(l)



Oxides of nitrogen NOx - NO, N2O and NO2

Origin • combination of atmospheric nitrogen andoxygen under high temperature

Effect • aids formation of photochemical smog which is irritating to eyes, nose, throat

• aids formation of low level ozone which affects plants and is irritating to eyes, nose and throat

Process sunlight breaks oxides NO2 —> NO + Oozone is produced O + O2 —> O3



Unburnt hydrocarbons CxHy

Origin • hydrocarbons that have not undergone combustion

Effect • toxic and carcinogenic (cause cancer)


POLLUTANT FORMATIONPOLLUTANT FORMATION

Nitrogen combines with oxygenN2(g) + O2(g) —> 2NO(g)

Nitrogen monoxide is oxidised2NO(g) + O2(g) —> 2NO2(g)

Incomplete hydrocarbon combustionC8H18(g) + 8½O2(g) —> 8CO(g) + 9H2O(l)


POLLUTANT REMOVALPOLLUTANT REMOVAL

Oxidation of carbon monoxide2CO(g) + O2(g) —> 2CO2(g)

Removal of NO and CO2CO(g) + 2NO(g) —> N2(g) + 2CO2(g)

Aiding complete hydrocarbon combustionC8H18(g) + 12½O2(g) —> 8CO2(g) + 9H2O(l)

CATALYTIC CONVERTERSCATALYTIC CONVERTERS

REMOVAL OF NOx and COREMOVAL OF NOx and CO

• CO is converted to CO2

• NOx are converted to N2

2NO(g) + 2CO(g) —> N2(g) + 2CO2(g)





2NO(g) + 2CO(g) —> N2(g) + 2CO2(g)

• Unburnt hydrocarbons converted to CO2 and H2O

C8H18(g) + 12½O2(g) —> 8CO2(g) + 9H2O(l)





2NO(g) + 2CO(g) —> N2(g) + 2CO2(g)

• Unburnt hydrocarbons converted to CO2 and H2O

C8H18(g) + 12½O2(g) —> 8CO2(g) + 9H2O(l)

• catalysts are rare metals - RHODIUM, PALLADIUM

• metals are finely divided for a greater surface area - this provides more active sites


STAGES OF OPERATIONSTAGES OF OPERATION



Adsorption • NO and CO seek out active sites on the surface• they bond with surface

• weakens the bonds in the gas molecules

• makes a subsequent reaction easier



Reaction • being held on the surface increases chance of favourable collisions

• bonds break and re-arrange



Desorption • products are released from the active sites



Adsorption Reaction Desorption



Adsorption • NO and CO seek out active sites on the surface• they bond with surface

• weakens the bonds in the gas molecules

• makes a subsequent reaction easier

Reaction • being held on the surface increases chance of favourable collisions

• bonds break and re-arrange

Desorption • products are released from the active sites

©2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING©2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING

THE ENDTHE END

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CHEMISTRY OF THE AIR KNOCKHARDY PUBLISHING 2008 SPECIFICATIONS