Enthalpy Changes delta h Nuclear Power 13.7: The Gibbs Free Energy Chemistry LibreTexts 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 Standard enthalpy of vaporization (vapH) for water at 100C is 40.66 kJ.. Confusion about enthalpy and when to use h = m(Cp)(delta T) Do I have to use one or the other in this case? : r thermodynamics