Usually when heat is added or extracted from a system the temperature changes. There are certain situations when the addition or subtraction of heat from a system does not result in a temperature change. In these situations the heat that is added or extracted is being converted into energy to effectuate a phase change from one physical state to another. This heat, the heat required to change a substance from one form to another, is known as the latent heat. It is the enthalpy change that accompanies a phase change at constant temperature and pressure. It is called latent because it is somewhat hidden from detection except for the physical change in a substance's form. The value of latent heat is dependent upon the exact nature of the phase change as well as on the specific properties of the substance. Latent heat is usually expressed in...