How much energy in kilojoules is required to convert 155 mL of water at its boiling point from liquid to vapor delta H vap H20 equals plus 40.7 kilojoules per mole?

The density of water @ 100oC (boiling point) is about 0.958 g/ml. First we need to convert the 155 ml to mass by multiply by the density.

155 ml * (0.958 g/ml) = 148.49 grams

Next convert the grams to moles by dividing by the molecular weight of water, which is 18 g/mol:

148.49 grams /(18 g/mol) = 8.25 mol of H2O

Finally multiply the moles of water by the heat of vaporization (Hvap) to get the final answer:

8.25 mol * (40.7 kJ/mol) = 335.775 kJ