1. Starter:
What is a change of state?

2. Lesson goals…
Describe melting, boiling (the difference between boiling and evaporation will come later).
Describe condensation & solidification.
Explain latent heat of vaporisation & latent heat of fusion including specific latent heat.
Describe experiments to measure the latent heats using steam and ice.
Know and be able to use the equation E=mL

3. Each change of state has a name:
Adding heat energy
Removing heat energy
Liquid
Melting
Boiling
Freezing
Condensing
Sublimation
Solid
Gas

4. Changes of state Example water:
There are three states or phases, solid (ice), liquid or gas (water vapour).
Energy is needed (taken in) or given out when a change of state occurs.
The melting point is the temperature at which the solid changes phase to become a liquid.
The boiling point is the temperature where the liquid changes phase to a gas.

5. This flat line shows where energy is being used to push the particles further apart and break the final intermolecular bonds
Temp/OC
This slope shows how energy is being used make molecules vibrate more and move faster so further increasing the KE of molecules
150
100 50
-50
This slope show how energy is being used make molecules move faster – NO intermolecular bonds left
This slope shows how energy is being used make molecules vibrate more and so increase KE of molecules
Is this a heating curve for ice?
Write a description of what is happening at each stage of this heating curve.
You also need to estimate /calculate energy input needed at each stage on graph
Time/s
This flat line shows where energy is being used to break intermolecular bonds – this has to be done during melting

6. LATENT HEAT Energy needed to break bonds and melt or boil
a material is known as
LATENT HEAT
Hidden:
Additional heat energy doesn’t show
as temperature change
Specific:
Just as for heat capacity, the specific latent heat is the energy needed to change the state of 1kg of the material.

7. Latent heat of fusion

8. Latent heat of fusion
During the melting time energy is supplied to the ice causing it to change phase. The energy absorbed is called the latent heat of fusion.
Ice has a specific latent heat of fusion of J/kg

9. Latent heat of vaporisation
At the boiling point, the energy is used to change from a liquid to a gas.
The latent heat of vaporisation for water is J/kg
Why do you think more energy is needed to change state from a liquid to a gas?

10. To calculate the energy needed to change state…
𝐸𝑛𝑒𝑟𝑔𝑦 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟𝑟𝑒𝑑=𝑚𝑎𝑠𝑠 𝑥 𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑙𝑎𝑡𝑒𝑛𝑡 ℎ𝑒𝑎𝑡
𝐸𝑛𝑒𝑟𝑔𝑦 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟𝑟𝑒𝑑=𝑚𝐿
Example: If 2kg ice is melted (at 0oC):
Energy transferred = mL= 2 x J/kg
= J
Question
How much energy is needed to change
10kg ice into water at the same temperature?
10k water into water vapour at the same temperature?

11. Answers 10 kg ice to water E = mL = 10 x 330 000 = 3 300 000 J
b. 10 kg water to water vapour
E = mL = 10 x
= J

12. A jeweller wants to melt 100 g of silver
A jeweller wants to melt 100 g of silver. The specific latent heat of fusion for silver is J/kg. How much energy will be required?
Energy = mass x specific latent heat
m = 100g = 0.1 kg
L = 100,000J/kg
E =mL
E =0.1 x
=10 000J
= 10kJ

13. Extension: What about sulphur?
Sulphur sublimes, why do you think that might be?

14. Experiment to measure the specific latent heat of fusion
Method: Heat the ice with the electric heater. Collect at least 30 ml water Weigh the water collected. Knowing the energy supplied to the ice (from the energy meter) use the equation E = mL to calculate L, the specific latent heat of fusion for water.

15. Results: Mass of dry 100ml beaker = ____________
Mass of 100ml beaker and water = _______
Mass of water = _____________
Energy supplied to ice = ________________
E = mL
L (specific latent heat of fusion ice) = _____
Why is this result approximate?

16. Specific latent heat of vaporisation of water
One method to measure the specific latent heat of vaporisation of water Measure the change in mass of boiling water over a fixed period of time (e.g. 500s) and the energy supplied to the boiling water by the electric heater. E = mL L= E/m This result is approximate, why?

17. Name that key term...

18. The amount of energy required to raise the temperature of 1kg of a substance by 1˚C

19. The temperature at which a substance turns from liquid to gas

20. These are present in solids and liquids but not in gases

21. A picture that uses colour to represent different temperatures

22. The point reached when all temperatures are equal

23. Occurs throughout the liquid
BOILING
EVAPORATION
A process in which a substance changes its state from the liquid state to the gaseous state
A process in which a substance changes its state from the liquid state to the gaseous state without boiling
Fast
Slow
Bubbles are formed
No bubbles formed
Occurs throughout the liquid
Takes place only from the exposed surface of the liquid
Occurs at a definite temperature – Boiling point
Occurs at all temperature
 Source of energy needed
 Energy supplied by surroundings