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Latent heat

When a substance changes from one state to another energy is either absorbed or liberated. This heat energy is called the latent heat, and part of it is the energy used to overcome the forces of attraction between the molecules.

The specific latent heat is the energy required to change the state of 1 kg of the substance

The specific latent heat of fusion of a solid is the heat energy needed to change 1 kg of the material in its solid state at its melting point to 1 kg of the material in its liquid state, and that released when 1 kg of the liquid changes to 1 kg of solid

The specific latent heat of vaporisation of a liquid is the heat energy needed to change 1 kg of the material in its liquid state at its boiling point to 1 kg of the material in its gaseous state, and that released when 1 kg of vapour changes to 1 kg of liquid

It is important to realise that no temperature change occurs during the change of state. The temperature will only rise or fall when the entire specimen has changed from one state to the other.

 
 
 
© Keith Gibbs 2011