enthalpies of melting and boiling for pure elements versus temperatures of transition, demonstrating trouton's rule
the enthalpy of fusion of a substance, also known as (latent) heat of fusion is the change in its enthalpy resulting from providing energy, typically heat, to a specific quantity of the substance to change its state from a solid to a liquid, at constant pressure. for example, when melting 1 kg of ice (at 0 °c under a wide range of pressures), 333.55 kj of energy is absorbed with no temperature change. the heat of solidification (when a substance changes from liquid to solid) is equal and opposite.
this energy includes the contribution required to make room for any associated change in volume by displacing its environment against ambient pressure. the temperature at which the phase transition occurs is the melting point or the freezing point, according to context. by convention, the pressure is assumed to be 1 atm (101.325 kpa) unless otherwise specified.