Water Enthalpy and Entropy vs. Temperature Solved Hvap = heat of vaporization = constant R= gas Chegg.com Heat of Sublimation Chemistry LibreTexts Vaporization enthalpy of isooctane (2,2,4 trimethylpentane). The fitted Download Scientific Diagram Delta_{vap}H^ for water is +40.49 kJ moi^ 1 at 1 bar and 100C . Change in internal energy for this vaporization under same condition is Sarthaks eConnect Largest Online Education Community 5) For vaporization of water at 1 bar, \Delta H = 40.63 \mathrm {kJ} \ma..