When a material changes phase from solid to liquid, or from liquid to gas, a certain amount of energy is involved in this change of phase. Latent Heat is use for change physical phase, during the this time temperature will not change. Heat of fusion: The heat required to change `1.0\ kg` of as substance from the solid to the liquid state is called the heat of fusion. Heat of vaporization: The heat required to change a substance from the liquid to the vapor phase is called the heat of vaporization.