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Do Now

•Write down three thing you need to do to work safely in a science laboratory

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SPECIFIC HEAT CAPACITY

Outcomes:•Understand that different materials require different amounts of energy to increase their temperature.•Know the equation.•Be able to use the equation.•Be able to describe an experiment to measure heat capacity.

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Copy this Glossary

absorber – A material that takes in thermal radiation.

conduction – The method of heat transfer in solids.

conductor – A material that lets heat flow through it.

convection – The method of heat transfer in fluids, which occurs because hot fluids are less dense than cold fluids.

emitter – A material that gives out thermal radiation.

free electrons – Electrons in a metal that are free to move through the metal.

heat transfer – The flow of heat energy from a hotter area to a colder area.

radiation – Heat energy transferred by infrared waves. This method of heat transfer does not need particles.

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How does energy affect materials?

Do different materials need the same amount of energy to increase their temperature by the same amount?

To increase the temperature of 1 kg of water by 1°C, requires 4200 J.

To increase the temperature of 1 kg of copper by 1°C, requires 390 J.

Water and copper require different amounts of energy because they have different values for a property called specific heat capacity.

and for copper is 390 J/kg°C.

It is the amount of energy required to increase the temperature of 1 kg of a material by 1°C.

So, the specific heat capacity for water is 4200 J/kg°C

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What is specific heat capacity?

The specific heat capacity of a material is the amount of energy required to raise 1 kg of the material by 1 °C.

Energy is measured in joules (J).

It can be used to work out how much energy is needed to raise the temperature of a material by a certain amount:

energyspecific heat

capacitytemperature

change= mass x x

Mass is measured in kilograms (kg).

Temperature change is measured in °C.

Specific heat capacity is measured in J/kg/°C.

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Calculations using S.H.C.

Energy absorbed = Mass x Specific Heat capacity x Temp rise

 

The Mr McT equation

E = mcΔT

J kg

J/kg/°C °C

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For example

0.5 kg of olive oil is heated until its temperature rises by 120 K. If the specific heat capacity of olive oil is 1970 J/kg/°C, how much heat energy was used?

Energy absorbed = Mass x Specific Heat capacity x Temp rise

Energy absorbed = 0.5 x 1970 x 120

Energy absorbed = 118200 J

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Practical

A

V12V

A metal

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Go through Practical worksheet

Follow instructions.Take measurements and do calculations.

All students must complete the lab sheet

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Measuring SHCs

• Energy put IN to metal = voltage x current x time• Energy = mass x specific heat capacity x temp

rise

voltage x current x time = mass x specific heat capacity x

temp rise

Specific heat capacity = (voltage x current x time)/(mass x temp rise)

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Specific heat capacity example

Using the specific heat capacity of water (4200 J/kg°C), how much energy is needed to increase the temperature of 600 g of water by 80°C in a kettle?

energy = 0.6 x 4200 x 80

= 201 600 J

Note: mass = 600 g = 0.6 kg

energyspecific heat

capacitytemperature

change= mass x x

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Do nowSpecific heat

questionsQ5 June 2005

Latent heat

Learning today • Use the terms latent heat of fusion

and give a molecular interpretation of latent heat

• Describe an experiment to measure specific latent heats for ice

• Test Sunday 1st April 2012• I will collect your books on

Monday

Latent Heat

Latent heat

In a change of state experiment, from the graph you will notice a flat spot the temperature of the salol stopped changing as the salol changed from a liquid to a solid.

Temp (°C)

Time (mins)

Melting point

Specific Latent heat “latent” = “hidden”

Why does

this happen?

Specific Latent heat - Copy When a substance changes from solid to liquid or from

liquid to gas, it takes energy to change its state. Heat is needed to break the bonds or separate the molecules. The temperature remains the same. When a liquid changes back to a solid energy is released again as the bonds form again.

solid to liquid increasing their potential energy instead of raising the temperature (kinetic energy

Temp (°C)

Time (mins)

Melting point

solid

liquid

Specific Latent heat - copy

The specific latent heat of a substance tells us how much energy is needed to change the state of 1 kg of substance at constant temperature.

Solid to liquid/liquid to solid

or

liquid to gas/gas to liquid

Specific Latent Heat

The specific latent heat of fusion (melting) of ice at 0 ºC, for example, is 330000 J.kg-1. This means that to convert 1 kg of ice at 0 ºC to 1 kg of water at 0 ºC,

330000 J of heat must be absorbed by the ice.

1 kg 1 kg

334000 J absorbed

All at 0°C

Specific Latent Heat

Conversely, when 1 kg of water at 0 ºC freezes to give 1 kg of ice at 0 ºC, 330000 J of heat will be released to the surroundings.

330000 J released

1 kg 1 kgAll at 0°C

Specific Latent Heat -Copy

Energy = mass x specific latent heat

J kg J/kg

E = mL

Specific Latent heat LE = m L

Do Now question 1 page 119

Learning today • Use the terms latent heat of fusion

and fusion and give a molecular interpretation of latent heat

• Describe an experiment to measure specific latent heats for ice and steam

•Test Sunday 1st April 2012• I will collect your books Today

Specific Latent Heat of Fusion Experiment

• Readings required • Energy supplied by heater• Energy = Power x time• Time = • Energy = VIt• Mass of water • E = mL

• Latent heat = Energy supplied . mass of water

Specific Latent Heat of Fusion Experiment • Energy = Power x time• Time =• Energy = VIt =

• Mass of water =

• E = mL• L = E /m• Latent heat = Energy supplied

. mass of water

Task- Evaluation

• What are the limitations in our method?• What solutions can you think of?• Why do we wait until the water is

dripping?• Does all the heat come from the heater?• Does all the ice remain in the funnel?• Now do Q4 Nov 2005

Markscheme4 (a) •turn on heater and wait until water starts dripping in beaker•empty beaker & replace, start watch•stop watch & remove beaker at same time•record time•find and record mass of water in beaker

(b) 60 x t = 120 x 340 t = 680 s

(c) (i) ice gains heat from surroundings/ice falls through funnel

(ii) lag or fit lid to funnel/place gauze in funnel bottom

Specific Latent Heat of Fusion Experiment

Latent heat

Now doNov 2005

Q5

Specific Latent Heat of Vaporisation - Copy

For water at its normal boiling point of 100 ºC, the latent specific latent heat of vaporisation is 2260000 J/kg. This means that to convert 1 kg of water at 100 ºC to 1 kg of steam at 100 ºC, 2260000 J of heat must be absorbed by

the water. vice verse for vapour to liquid

All at 100°C

2260000 J input

1 kg 1 kg

Specific Latent Heat of Vaporisation

Conversely, when 1 kg of steam at 100 ºC condenses to give 1 kg of water at 100 ºC, 2260 kJ of heat will be released to the surroundings.

All at 100°C

2260000 J released

1 kg 1 kg

Specific Latent Heat of Steam

Latent Heat

Specific Latent Heat -Copy

Energy = mass x specific latent heat

J kg J/kg

E = mL