Dear PF Forum, As per wiki: https://en.wikipedia.org/wiki/Standard_enthalpy_change_of_formation_(data_table) Standard enthalpy of water: Gas: -241.818 kJ/mol Liquid: -285.8 kj/mol What does it means? That to produce H2O per mol at 1000C, it releases 241.818 kJ. That to produce H2O per mol in liquid, it releases 285.5 kJ. Because in liquid water is not 1000C, (say 250C), so actualy the difference 43.682kJ is to increase the temperature to 1000C?. Is that what it means? And what temperature is the gas? What temperatur is the liquid? Thank you very much.