1. 4.3.3 Thermal properties of materials

2. (a) define and apply the concept of specific heat capacity
Objective
(a) define and apply the concept of specific heat capacity

3. (b) select and apply the equation E = mcΔθ
Objective
(b) select and apply the equation E = mcΔθ

4. Specific Heat Capacity
If we heat matter so that its temperature rises, the amount of energy we must supply depends on three things:
The mass m of the material
The temperature rise Δθ we wish to achieve
The material itself

5. Specific Heat Capacity
ΔQ = mcΔθ
where
ΔQ = energy supplied (J)
m = mass (kg)
c = specific heat capacity (J kg-1 K-1)
Δθ = change in temperature (°C or K)

6. Specific Heat Capacity
The specific heat capacity of a substance is numerically equal to the amount of energy required to raise the temperature of 1kg of the substance by 1 K (or by 1 °C)

7. Specific Heat Capacity
When J of energy is supplied to a 2kg block of aluminium, its temperature rises from 20 °C to 35 °C. Find the specific heat capacity of aluminium.
c = ΔQ / mΔθ
c = J / (2 kg x 15 K)
c = 880 J kg-1 K-1

8. Specific Heat Capacity
How much energy must be supplied to raise the temperature of 5 kg of water from 20°C to 100°C?
Which requires more energy, heating a 2 kg block of lead by 30 K, or heating a 4 kg block of copper by 5 K?
A well-insulated 1 kg block of iron is heated using a 50 W heater for 5 min. Its temperature rises from 22°C to 55°C. Find the specific heat capacity of iron.

9. Objective
c) describe an electrical experiment to determine the specific heat capacity of a solid or liquid

10. SHC Practical Run for 1200 seconds Take temperature every 30 s
heater
thermometer
Run for 1200 seconds
Take temperature every 30 s
Draw graph
Calculate c
Repeat for different substance
metal block

11. SHC Practical calculate gradient Δθ Δt E = mc Δθ Δt Δt
P = m x c x gradient
P = VI
c = P
m x gradient
θ (°C)
t (s)

12. SHC Practical

13. Objective
d) describe what is meant by the terms latent heat of fusion and latent heat of vaporisation

14. Specific Latent Heat What is happening at: AB? CD?
100 D θ
AB: Melting – particles becoming disordered
CD: Boiling – particles completely separating A B O t

15. Specific Latent Heat
At AB and CD, energy is being input, but the temperature isn’t rising
The energy is being used to break the molecules free, not raise the temperature

16. Specific Latent Heat At AB (melting) and CD (boiling) energy input
temperature does not change
molecules become disordered (AB) or separate from each other (CD)
little change in kinetic energy
electrical potential energy increases

17. Specific Latent Heat At OA and BC and DE energy input
temperature rises
molecules move faster
kinetic energy increases (temperature = average ke)
little change in electrical potential energy

18. Specific Latent Heat
The energy needed to cause this change of state is Latent Heat (“Latent” means “hidden”)
When a substance melts, this is the latent heat of fusion
When a substance boils, this is the latent heat of vaporisation

19. Definitions
Latent heat of fusion is the energy which must be supplied to cause a substance to melt at a constant temperature
Latent heat of vaporisation is the energy which must be supplied to cause a substance to boil at a constant temperature

20. Specific Latent Heat Remember:
Temperature is a measure of the average kinetic energy of the molecules
When a thermometer is put into water, the water molecules collide with the thermometer and share their kinetic energy with it.
At a change of state, there is no change in kinetic energy, so no change of temperature

21. Specific Latent Heat
Why does it take more energy to boil a substance than it does to melt it?
Melting – molecules still bonded to most of their neighbours – breaks one or two bonds
Boiling – each molecule breaks free from all of its neighbours – breaks eight or nine bonds

22. Specific Latent Heat
The specific latent heat of a substance is the energy required per kilogram of the substance to change its state without any change of temperature

23. Specific Latent Heat
The specific latent heat of vaporisation of water is 2.26 MJ kg-1. Calculate the energy needed to change 2.0 g of water into steam at 100 °C.
1.0 kg (1000 g) of water requires 2.26 MJ of energy
Therefore,
energy = 2.0/1000 x 2.26 x 106
= 4520 J

24. Specific Latent Heat
The specific latent heat of fusion of water is kJ kg-1. Calculate the energy needed to change 2.0 g of ice into water at 0 °C.
1.0 kg (1000 g) of ice requires 330 kJ of energy
Therefore,
energy = 2.0/1000 x 3.30 x 105
= 660 J

25. Practical