Edition 7 number 4F11

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

Hedi Zappacosta 1E
Posts: 66
Joined: Fri Sep 28, 2018 12:27 am

Edition 7 number 4F11

"Q4A. 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?"

I got the answer right, but I was wondering why it was ok for us to ignore the number of moles of N2 gas in this case in the entropy equations.

Nico Edgar 4L
Posts: 32
Joined: Fri Sep 28, 2018 12:19 am

Re: Edition 7 number 4F11

I am not entirely sure why it was ok to ignore the moles of N2 gas. It might be because we are at ideal conditions and can just assume it is 1? But, in example 4F5 they also ignore the moles and point to the eqaution delta S= C ln(T2/T1). I think it is because we treat the heat capacity as constant in the temperature range.

Nico Edgar 4L
Posts: 32
Joined: Fri Sep 28, 2018 12:19 am

Re: Edition 7 number 4F11

Also I can't seem to get the right answer. Do we find the Entropy change through temperature and then the Entropy change through Volume and sum them?

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