The enthalpy of vaporization (symbol Hvap), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy (enthalpy) that must be added to a liquid substance to transform a quantity of that substance into a gas. The enthalpy of vaporization is a function of the pressure at which that transformation takes place. DeltaHvap is a way to measure intermolecular forces quantitatively.

Calculate the amount of energy (in kilojoules) needed to cool 465 g of water vapor from 140oC to -10 oC. Assume that the specific heat of water is 4.184 J/g oC over the entire liquid range and the specific heat of steam is 1.99 J/g oC. The DeltaHvap for water is 40.79 kJ/mol. The DeltaHfus = 6.01 kJ/mol