Question

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

(a) 25 J

(b) 37 J

(c) 44 J

(d) 51 J

I have been asked this question in my homework.

My doubt is from Applications of Humidity Chart topic in section Humidity Charts & their Use, Analysis of the Degrees of Freedom in a Steady – State Process, Solving Material and Energy Balances Using Process and Unsteady State Material and Energy Balances of Basic Chemical Engineering

Answer 1

Correct answer is (b) 37 J

The best explanation: ∆H = 5(25 – 20) + 0.2*[10(25 – 20) + 10] = 25 + 12 = 37 J.