Latent Heat

The latent heat of a substance is defined as the amount of heat absorbed by a unit mass of the substance to change its state without change of temperature. The heat absorbed during the change of state of a substance is used to overcome the force of attraction between the molecules of a substance. The kinetic energy of the molecules does not increase and hence there is no raise in temperature during the change of state of the substance. Two of the more common forms of latent heat (or enthalpies or energies) encountered are latent heat of fusion (melting or freezing) and latent heat of vaporization (boiling or condensing). These names describe the direction of energy flow when changing from one phase to the next: from solid to liquid, and to gas.