Homework Help: Calculate the heat capacity at constant volume and constant pressure.

1. Sep 18, 2011

LogicX

1. The problem statement, all variables and given/known data

I am given the amount of moles of gas, how many joules of heat I put into the system, and a positive change in temperature. Then it says "calculate the molar heat capacities at constant volume and constant pressure of the gas."

2. Relevant equations

q=CT, C(constant pressure)-C(constant volume)=nR, U= q+w, H=U+PV

3. The attempt at a solution

I just don't know how to do this problem without knowing whether the temperature change occurs at constant volume or constant pressure. If I knew either of those the problem would be easy.

I have q and delta(T), so I should be able to calculate a heat capacity. But I don't know which one it would be.

2. Sep 19, 2011

Staff: Mentor

Can you give exact wording of the question? Perhaps the information is there, just hidden?

3. Sep 19, 2011

LogicX

"When 178 J of energy is supplied as heat to 1.9 mol of gas molecules, the temperature of the sample increases by 2.55 K. Calculate the molar heat capacities at constant volume and constant pressure of the gas."

4. Sep 19, 2011

Staff: Mentor

Nah, you are right - question is unclear.

5. Sep 19, 2011

LogicX

Ok thanks, I'll go talk to my professor tomorrow.

6. Sep 20, 2011

LogicX

Well my professor is a senile old man so I tried to ask him today, but he seemed to have a mental block against admitting he wrote the question wrong so at first he tried to tell me I can assume the pressure is constant, then that I can assume that the volume is constant.

I guess I just have to hope that he doesn't pull this **** on the exam because he would probably just arbitrarily pick one that he wanted us to assume was constant and if I confronted him about it get the same talking in circles answer that I got just now.

I hate college sometimes.