<P> 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 , ( or resulting from the release of energy from a substance during transition from liquid to solid ) , at constant pressure . ( It is used to decribe the change in phase of matter of melting or freezing ) . 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 . </P>
the heat required to change 1 gram of a solid at its normal melting point
The enthalpy of fusion of a substance , also known as ( latent ) heat of fusion