Solved] 1. The boiling point of propane at 1 atm (14.7 psi) pressure is 42.0 C and its H(vap) is 18.8 kJ mol. R = 8.314 Course Hero Use Hess's law to prove that Delta subH = Delta vapH + Delta fusH. Homework.Study.com If \Delta {H}{vap }^{\circ} for {H}{2} {O} is 44 {kJ} {mol}^{ 1}, then amount of heat required to evaporate 9 {~g} of {H}_{2} {O} is : The enthalpy of vaporization of \mathrm{H}{2} \mathrm{O}(1) is x \mathrm{~kJ} \mathrm{mol} and enthalpy of formation of water vapour \mathrm{ykJ} \mathrm{mol}. Enthalpy of formation of Confusion about enthalpy and when to use h = m(Cp)(delta T) Do I have to use one or the other in this case? : r thermodynamics