Enthalpy of Vaporisation
The enthalpy change when one mole of a liquid becomes vapour at its boiling point.
Formula / equation
ΔH_vap
Unit
kJ/mol
In depth
Vaporisation must overcome intermolecular forces completely, so it is always strongly endothermic and typically several times larger than the enthalpy of fusion. Hydrogen-bonded liquids have exceptionally high values, which is why water is such an effective coolant.
Examples in the real world
Water requires 40.7 kJ/mol against ethanol's 38.6 and methane's mere 8.2.