The amount of heat lost or gained per gram of water is expressed in calories of latent heat. The latent heat of fusion , the heat released as water is converted from liquid to solid, is 80 calories per gram of water. The reverse reaction, the conversion of ice to water described above, absorbs 80 calories of heat for each gram of water converted from a solid to a liquid state. Release or absorbtion of latent heat occurs during changes of state in water. Two of these processes, evaporation and condensation, occur over large areas of Earth's surface and contribute significantly to the generation of weather phenomena and the redistribution of heat on the earth's surface.
Liquid water is converted to water vapor during evaporation .
Heat is absorbed to convert the liquid to a less ordered form. This is a function of the number of bonds that must be broken or modified between water molecules.