3 Ways to Calculate Vapor Pressure wikiHow Heat of Vaporization from Vapor Pressure (Example) The difference between `Delta`H and `Delta`U at constant volume is equal to Standard enthalpy of vapourisation `Delta_("vap")H^( )` for water at `100^@C` is `40.66 kJ mol^( 1)`. The internal energy of vapourisation of water at `100^@C` (in kJ `mol^( 1)`) is (Assume water vapour to behave like 5 gram Delta 8 Disposable THC HHC Vape Pen with Preheat 4asvapes Vaping Products Solved Heat, q, is energy transferred between a system and Chegg.com