What is the enthalpy change of 20oC system if the heat capacity of air at 25oC is 5 J/oC and heat capacity of water vapor at 25oC is 10 J/oC, enthalpy of vaporization is 10 J, and the humidity is 20%?

Correct Answer: 37 J
∆H = 5(25 – 20) + 0.2* = 25 + 12 = 37 J.