Latent Heat (AQA GCSE Physics): Revision Notes
3.2.3 Latent Heat
When a change of state happens, energy is required. This energy required to change the state of a substance is called latent heat.
When a change of state involving heating occurs, such as boiling or melting, this energy supplied to the system increases the internal energy. The substance changes state only and does not change in temperature. This is because the energy is being used to break apart the bonds between particles in the substance, and is not increasing the temperature.
When a change of state involving cooling occurs, such as condensation or freezing, the system decreases in internal energy. This is because energy is being released to make bonds between the particles. Again, the latent heat does not change the temperature, it only changes the state.