Latent Heat of Vaporization:
The amount of heat required by the unit mass of a liquid to change into its vapor at a constant temperature is called the latent heat of vaporization of the liquid.
For any substance, the latent heat of vaporization is the latent heat of condensation. It is denoted by L. Thus if a quantity H of heat is given or extracted to change the state of mass m, for vaporization or condensation respectively then, H = mL.
Unit of L in SI system is J.kg-1.
Latent Heat of Condensation:
The amount of heat extracted from the unit mass of vapor to change it into its liquid state at a constant temperature is called the latent heat of condensation.