3 Ways to Calculate Vapor Pressure wikiHow Law of Equipartition of Energy Energy is equally distributed among all degrees of freedom Each degree contributes kT per molecule Translational, rotational, Standard Enthalpy of Formation, \(\Delta H_{\rm f}^\circ \) For water vap H = 41 kJ mol^1 at 373 K and 1 bar pressure. Assuming that water vapour Sarthaks eConnect Largest Online Education Community Standard enthalpy of vaporization (vapH) for water at 100C is 40.66 kJ..