Thursday
May 5, 2016

# Homework Help: Chemistry - Science (Dr. Bob222)

Posted by Ana on Thursday, May 8, 2014 at 8:44am.

Nitrogen gas has values of Cv and Cp of 20.8 and 29.1 J K-1 mol-1, respectively. When a certain amount of nitrogen is heated at constant pressure, what fraction of the heat Q is used to increase the internal energy of the gas, and how is the remaining energy used?

A) 3/2 of Q is used to increase internal energy, the rest used for work.
B) All of Q is used to increase the internal energy of the gas and there is no remaining energy.
C) ~ 0.7 (70%) of Q is used to increase the internal energy and the rest goes to pressure-volume work.
D) Most of Q is used up as work in the expansion of the gas at constant pressure.
E) 58% of Q does work, and the rest goes to increasing the internal energy of the gas.
• Chemistry - Science (Dr. Bob222) - DrBob222, Thursday, May 8, 2014 at 3:32pm

Thermodynamics is not my field. I would go with C but get a second opinion.
I don't think A is right because for a diatomic gas Cp is 7/2R.
B. B can't be right because at constant P there will be pdV work.
C. The difference between Cv and Cp is 8.3 and that is about 28.5% of 29.1 so that much energy goes to work leaving about 71.5% for heat and that's close to 70%.
D. Doesn't sound reasonable
E. I tried various manipulations to get 58% and couldn't do it so I don't know how they arrived at this as a possible answer.
I would be interested in knowing the correct answer (and WHY of course) if it isn't C.