phase diagram water.svg Enthalpy of vaporization Wikipedia The enthalpy of vaporization of \mathrm{H}{2} \mathrm{O}(1) is x \mathrm{~kJ} \mathrm{mol} and enthalpy of formation of water vapour \mathrm{ykJ} \mathrm{mol}. Enthalpy of formation of What is `Delta U` when `2.0` mole of liquid water vaporises at `100^(@)C`? The heat of vaporisation `(Delta H_("vap".))` of water at `100^(@)C` is `40.66 KJmol^( 1)`.