Interactions of water Interactions of water and Energyand Energy

Questions:Questions: On cool fall mornings On cool fall mornings

when you drive passed when you drive passed the harbour, you the harbour, you sometimes will see sometimes will see steam rising off the steam rising off the water. water.

Why?Why?

Does water or air cool Does water or air cool down faster?down faster?

Different substances Different substances change temperature at change temperature at different ratesdifferent rates

Why? Why?

Earth Earth

Only 30% of the earth’s surface is Only 30% of the earth’s surface is landland

Therefore most of the incoming solar Therefore most of the incoming solar radiation that gets past the radiation that gets past the atmosphere hits wateratmosphere hits water

The interactions between this solar The interactions between this solar energy and water are very important energy and water are very important to life on earthto life on earth

Interactions between Interactions between energy and water:energy and water:

The type of interaction depends on The type of interaction depends on the state of the water (s, l, g)the state of the water (s, l, g)

For example: For example:

fresh white snow reflects 90% of fresh white snow reflects 90% of radiationradiation

ice reflects 50% of radiationice reflects 50% of radiation

water reflects only 7%water reflects only 7%

Specific Heat CapacitySpecific Heat Capacity

The amount of heat The amount of heat needed to change needed to change the temperature by the temperature by 1°C for 1g of 1°C for 1g of substance.substance.

Each substance Each substance has a unique has a unique specific heat specific heat capacity.capacity.

SubstancSubstancee

s.h.capacits.h.capacityy

(J/g °C)(J/g °C)

Fresh Fresh waterwater

4.184.18

Ocean Ocean waterwater

3.893.89

AirAir 1.001.00

Specific heat capacity of Specific heat capacity of water:water:

Water has a relatively large spec. Water has a relatively large spec. heat capacityheat capacity

A larger specific heat capacity results A larger specific heat capacity results in a smaller temperature increasein a smaller temperature increase

This helps to moderate water’s This helps to moderate water’s temperature because water can temperature because water can absorb a large amount of energy with absorb a large amount of energy with only a small temperature changeonly a small temperature change

Moisture in the AirMoisture in the Air

Cold air can hold less moisture then Cold air can hold less moisture then warm airwarm air

Therefore when the air temperature Therefore when the air temperature is high, the amount of water vapour is high, the amount of water vapour can be highcan be high

Moist air takes a bit longer to cool Moist air takes a bit longer to cool then warm airthen warm air

SaturationSaturation

When there is as much water vapour When there is as much water vapour in the air as possible at any given in the air as possible at any given temperature, we say the air is temperature, we say the air is saturatedsaturated

What happens in the summer What happens in the summer when you bring a cold drink when you bring a cold drink

outside?outside? Lets say the air temperature is 26 degrees Lets say the air temperature is 26 degrees

Celsius. When the air is this warm it can Celsius. When the air is this warm it can hold a lot of water vapourhold a lot of water vapour

When you bring out the cold glass, the air When you bring out the cold glass, the air directly next to the class becomes colder.directly next to the class becomes colder.

This colder air can not hold as much water This colder air can not hold as much water vapour as the warmer air, so the water vapour as the warmer air, so the water “falls out”“falls out”

It “falls” onto the glass because that is a It “falls” onto the glass because that is a surface for the water droplets to form onsurface for the water droplets to form on

Read pages 431-432Read pages 431-432

Think about it and answer the Think about it and answer the questions on the sheetquestions on the sheet

Q=mcQ=mc∆∆TT

Q = energy absorbed (J)Q = energy absorbed (J) m = mass of substance (g)m = mass of substance (g) c = specific heat capacity of c = specific heat capacity of

substance substance (J/g)(J/g)

∆∆T = change in temperature (°C)T = change in temperature (°C)

Practice:Practice:1.1. What is the Q, if 5.2kg sample of What is the Q, if 5.2kg sample of

limestone has a change in temp. of limestone has a change in temp. of 16.3 °C?16.3 °C?

2.2. What is the change in temp, if a What is the change in temp, if a 9.2g sample of mud absorbs 950J of 9.2g sample of mud absorbs 950J of energy?energy?

3.3. An unknown sample absorbs 6000J An unknown sample absorbs 6000J and has a temp change of 62 °C. It and has a temp change of 62 °C. It has a mass of 2.6kg, what is the has a mass of 2.6kg, what is the specific heat capacity?specific heat capacity?

Heat of vaporization Heat of vaporization

liquid to gas requires energyliquid to gas requires energy

gas to liquid releases energygas to liquid releases energy

Heat of fusionHeat of fusion

solid to liquid requires energysolid to liquid requires energy

liquid to solid releases energyliquid to solid releases energy

Changes in state of water Changes in state of water sheetsheet

Sample problemSample problem

1.1. What is the heat absorbed (Q) if 2.0g water What is the heat absorbed (Q) if 2.0g water is heated from 10°C to 25°C ?is heated from 10°C to 25°C ?

Q=mcQ=mc∆∆TT

=2.0g x 4.18=2.0g x 4.18J/g °C J/g °C x (25 – 10 °C)x (25 – 10 °C)

=125.4 J=125.4 J

Remember J = joules, the unit for Remember J = joules, the unit for energyenergy