Heat of Vaporization from Vapor Pressure (Example) Delta H Vap Standard Enthalpy Of Atomization, Solution And Phase Transition 3. Using the approximate form of the Clausius Clapeyron The internal energy change (in J) when 90 g of water undergoes complete evaporation at `100^(@)C ` is ______ . (Given : `Delta H_("vap")` for water at 373 K = 41 kJ mol , `R = 8.314 JK^( 1) mol^( 1)`)