Up Learn – A Level physics (AQA) – THERMAL PHYSICS
Specific Latent Heat: Fusion and Vaporisation
Specific latent heat is latent heat per unit mass. Specific latent heat of fusion relates to a solid becoming a liquid, and specific latent heat of vaporisation relates to a liquid becoming a gas.
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Thermal Physics
2. Thermal Equilibrium (free trial)
3. Heating and Kinetic Energy (free trial)
4. What is Temperature? (free trial)
5. Defining Temperature (free trial)
6. Temperature Scales (free trial)
7. The Kelvin Scale(free trial)
8. Degrees Celsius to Kelvin (free trial)
2. States of Matter (free trial)
3. Intermolecular Forces (free trial)
4. Forces or Bonds? – Article (free trial)
5. What is Internal Energy? (free trial)
6. Thermal Energy and Internal Energy – Article (free trial)
7. Change in Internal Energy – Energy Transfer by Heating (Part 1) (free trial)
8. Change in Internal Energy – Energy Transfer by Heating (Part 2) (free trial)
9. Change in Internal Energy – Energy Transfer by Work (free trial)
10. Change in Internal Energy – Heating and Work (free trial)
11. ΔU = Q + W – Article (free trial)
12. Constant Internal Energy (free trial)
2. Factors Affecting Temperature Increase – Mass and Energy (free trial)
3. Factors Affecting Temperature Increase – Specific Heat Capacity (free trial)
4. Calculating Energy Required to Increase Temperature (free trial)
5. Objects in Thermal Equilibrium (free trial)
6. Worked Example – Calculating Temperature at Thermal Equilibrium (free trial)
7. Assumption of Energy Transfer (free trial)
8. Calculating c Using Gravitational Potential Energy (free trial)
9. Calculating c for a Solid using Electrical Energy (free trial)
10. Calculating c for a Liquid using Electrical Energy (free trial)
11. Calculating c Using Continuous Flow 1 (free trial)
12. Calculating c Using Continuous Flow 2 (free trial)
We’ve previously seen that latent heat is the energy transferred during a change of state without a change in temperature.
Now, the amount of energy transferred during a change of state depends on the material.
For example, it takes this many joules of energy to melt 1 kilogram of ice…
And it takes this many joules of energy to melt 1 kilogram of lead.
Now, another word for melting is fusion.
This might sound a bit counterintuitive, since we may normally think of a liquid fusing together to form a solid…
But fusion actually comes from the latin word ‘fundere’, which means ‘to melt’.
And so, we call the energy required to change 1 kilogram of material from the solid state to the liquid state without a change of temperature, the specific latent heat of fusion.
We add ‘specific’ before it because it’s defined for a particular unit mass of material
In this case, 1 kilogram!
Next, it takes this many joules of energy to turn liquid water into a gas…
And it takes this many joules of energy to turn liquid lead into a gas.
Now, the transition of a liquid into a gas is known as vaporisation.
And so, we call the energy required to change 1 kilogram of a material from the liquid state to the gas state without a change of temperature, the specific latent heat of vaporisation.
Finally, both the specific latent heat of fusion and the specific latent heat of vaporisation are the amount of energy required for a change of state per kilogram
The units for both are joules per kilogram.
So, for example, the specific latent heat of fusion of lead is this…
And the specific latent heat of vaporisation of water is this!
To sum up…
The energy required to change 1 kilogram of material from the solid state to the liquid state without a change of temperature is known as the specific latent heat of fusion
And the energy required to change 1 kilogram of a material from the liquid state to the gas state without a change in temperature is known as the specific latent heat of vaporisation
And the units for both are joules per kilogram.