Question 4F.11.

Volume: $\Delta S = nR\ln \frac{V_{2}}{V_{1}}$
Temperature: $\Delta S = nC\ln \frac{T_{2}}{T_{1}}$

Tiffany_Cacy_3D
Posts: 70
Joined: Fri Sep 28, 2018 12:24 am

Question 4F.11.

" During the test of an internal combustion engine, 3.00L of nitrogen gas at 18.5 degrees C was compressed suddenly (and irreversibly) to .500L by driving in a piston. In the process the temperature of the gas increased to 28.1 degrees C. Assume ideal behavior and 1.00 mole of nitrogen gas. What is the change in entropy of the gas?"
So I know you calculate the temperature and volume changes separately but in the solutions manual they used the equation Delta S=nRT(ln(T2/T1)). I don't understand why they used this because on our equation sheet the equation is Delta S=nCT(ln(T2/T1)). Why did they use R instead of C?

aisteles1G
Posts: 117
Joined: Fri Sep 28, 2018 12:15 am

Re: Question 4F.11.

I was also really confused by this but the only explanation I could see is that the problem did not state the the pressure was constant so it would technically be incorrect to assume this and use the Cp in that equation, therefore they used the one that does not depend on pressure

Nicole Elhosni 2I
Posts: 62
Joined: Fri Sep 28, 2018 12:28 am

Re: Question 4F.11.

You can assume pressure is constant because the question says the system expands irreversibly, which is an expansion process with constant pressure.