freezing

Change of state from liquid to solid, as when water becomes ice. For a given substance, freezing occurs at a definite temperature, known as the freezing point, that is invariable under similar conditions of pressure, and the temperature remains at this point until all the liquid is frozen; the freezing point and melting point of the substance are the same temperature. When a liquid freezes, the temperature of the solid-liquid mixture remains constant at the freezing point as heat is removed and more of the liquid becomes solid. Conversely, when heat is added, the temperature remains constant at the freezing point as the solid melts.

The amount of heat per unit mass that has to be removed to freeze unit mass of a substance (or to be added to melt it) is a constant for that substance, and is known as the latent heat of fusion.