Molar Enthalpy of Vaporization Definition

Molar enthalpy of vaporization is the amount of energy needed to change one mole of a substance from the liquid phase to the gas phase at constant temperature and pressure. The usual unit is kilojoules per mole (kJ/mol). Because energy is required to vaporize a liquid, molar enthalpy of vaporization has a positive sign. This indicates energy is absorbed by the system to get the molecules into the gas state. Molar Enthalpy of Vaporization Formula The mathematical formula used to calculate molar enthalpy of vaporization is: q n⋅ΔHvap q is the amount of absorbed heatn is the number of molesΔHvap is the molar enthalpy change of vaporization This equation is rearranged to give: ΔHvap q/n