Question

What is the enthalpy change of 10^oC system if the heat capacity of air at 20^oC is 5 J/^oC and heat capacity of water vapor at 20^oC is 15 J/^oC, enthalpy of vaporization is 10 J, and the humidity is 40%?

(a) 58 J

(b) 84 J

(c) 114 J

(d) 135 J

This question was addressed to me by my college professor while I was bunking the class.

Enquiry is from Applications of Humidity Chart topic in portion 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

Right option is (c) 114 J

The explanation: ∆H = 5(20 – 10) + 0.4*[15(20 – 10) + 10] = 50 + 64 = 114 J.