Calculating Energy Change Phase Change Easy Peasy All in One High School The enthalpy of vapourisation of liquid water using the data : `H_(2)(g)+1 2O_(2)(g)rarr H_(2)O(l) Standard enthalpy of vaporization (vapH) for water at 100C is 40.66 kJ.. Predicting the Enthalpy of Vaporization and Calculating the Entropy of Vaporization of 87 Octane Gasoline Using Vapor Pressure Solved: For the reversible vaporization of water at $$100^0C$$ and 1 atmospheric pressure, $$Delta [Physics] y= 8525.8x+23.536 1. From the slope of the trendline, Chegg.com