The Molar Enthalpy of Fusion is the amount of energy needed to change one mole of a substance from the solid phase to the liquid phase at constant temperature and pressure. And is denoted by ΔHfusion. Molar Enthalpy of Fusion is usually measured using the Kilojoule per Mole for Molar Enthalpy. Note that the value of Molar Enthalpy of Fusion is always positive.