Up Learn – A Level physics (AQA) – THERMAL PHYSICS
What is Latent Heat?
Latent heat is the energy transferred during a change of state without changing the temperature.
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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)
Back in Internal Energy, we looked at what happens when we add a heater to ice…
And we tracked its temperature over time on this graph.
For example, we saw that when the heater is turned on, the temperature of the ice initially increases
This is because the energy transferred by heating…
This is because the energy transferred by heating increases the average kinetic energy of the particles.
Then, at this point, the temperature stops increasing for a while…
And the ice turns into liquid water.
And so, here, the energy transferred by heating…
Here, the energy transferred by heating increases the average potential energy of the particles.
Now, we call the energy transferred during a change of state without changing the temperature, latent heat
Where latent means ‘hidden’, because when this energy is transferred, we don’t observe a temperature increase.
And so, if we continue to leave the heater on, and track what happens…
We can see that when energy is transferred to the material, the material changes from a solid, to a liquid, to a gas.
And conversely, when energy is transferred to the surroundings, the system changes from a gas, to a liquid, to a solid!
And this explains why we get worse burns from water vapour at 100 degrees Celsius than liquid water at 100 degrees Celsius.
When water vapour touches our skin, it turns back into liquid water.
So, as well as the energy transferred due to the temperature difference…
Energy is also transferred when the water changes from gas to liquid!
To sum up, latent heat is…
Latent heat is the energy transferred during a change of state without changing the temperature.