1. Changes of State and Latent Heat
You will be able to answer the following questions.
How do materials change state?
What is latent heat?
How can I calculate specific latent heat?
Describe how materials
change state.
Explain latent heat
Be able to calculate
latent heat

2. Changes of State Gas Boiling Sublimation Condensing Solidifying
Liquid
Solid
Boiling
Sublimation
Condensing
Solidifying
Melting
Describe how materials
change state.
Explain latent heat
Be able to calculate
latent heat

3. A mist appears on the inside of a window in a bus full of people.
Steam is produced from the surface
of the water in a pan when the
water is heated before it boils.
Ice cubes taken from a freezer thaw
out.
Water put into a freezer gradually
turns to ice.
Solid carbon dioxide turns to a gas.
Carbon dioxide gas turns into a
solid.
Freezing/
Solidifying
Melting
Vaporisation
Condensation
Condensation
Sublimation 29

4. Heating/Cooling Curves
To go from solid to liquid to gas, energy must be input.
This energy is required to break the bonds that hold molecules together.
Describe how materials
change state.
Explain latent heat
Be able to calculate
latent heat

5. Heating/Cooling Curves
Describe how materials
change state.
Explain latent heat
Be able to calculate
latent heat

6. Heating a metal from a solid to a liquid.
Latent Heat
Note that when the material is changing state, even though the amount of energy is still changing, temperature remains constant.
Example
Heating a metal from a solid to a liquid.

7. Latent Heat
As you heat the metal the atoms gain kinetic energy (vibrate more about their fixed position in the lattice) and the temperature of the metal increases.
When the metal starts to melt, energy is used to break the bonds.
So while the metal melts temperature remains constant.
The energy absorbed while melting is called the latent heat of fusion
Describe how materials
change state.
Explain latent heat
Be able to calculate
latent heat

8. Energy transferred = mass x specific latent heat of fusion
Equation
Just as with specific heat capacity, we can measure the latent heat per unit mass.
Energy transferred = mass x specific latent heat of fusion
E = mLf J kg
J/kg
Describe how materials
change state.
Explain latent heat
Be able to calculate
latent heat

9. Latent heat of vaporisation.
As boiling water is heated, the energy supplied is used to overcome the intermolecular forces holding the molecules together in a liquid state
Where there is a change in state without a change in temperature the energy involved is called latent heat.
Describe how materials
change state.
Explain latent heat
Be able to calculate
latent heat

10. This is known as the latent heat of vaporisation Lv.
The quantity of energy needed to vaporise a sample depends on the mass of the sample. As with heat capacity, comparisons can be made between different materials by measuring the energy needed to turn 1 kg of a material at its boiling point into vapour.
This is known as the latent heat of vaporisation Lv.
Describe how materials
change state.
Explain latent heat
Be able to calculate
latent heat

11. specific latent heat of vaporisation, L, can also be calculated using:
E=mLv
Units of L: J/kg.
Describe how materials
change state.
Explain latent heat
Be able to calculate
latent heat

12. Experiment: Measuring the Latent heat of Ice
Health and safety:
The heaters will be hot!
Describe how materials
change state.
Explain latent heat
Be able to calculate
latent heat

13. Diagram and concise method. Results. Analysis. Calculate L.
To complete:
Diagram and concise method.
Results.
Analysis. Calculate L.
Evaluation. Compare your results to the ideal value. What has caused these differences?
Lice = J/kg
Describe how materials
change state.
Explain latent heat
Be able to calculate
latent heat

14. Can you answer these Questions?
How do materials change state?
What is latent heat?
How can I calculate specific latent heat?
Describe how materials
change state.
Explain latent heat
Be able to calculate
latent heat