## 7th edition 4F.11

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

chloewinnett1L
Posts: 55
Joined: Fri Sep 28, 2018 12:20 am

### 7th edition 4F.11

I'm confused as to why the solutions manual doesn't indicate that you use (5/2)R instead of R when calculating the entropy change of non-isothermal irreversible expansion. Isn't the pressure kept constant? And the gas should be assumed ideal?

Chem_Mod
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### Re: 7th edition 4F.11

Please post the question too so we can better assist.

Theodore_Herring_1A
Posts: 60
Joined: Fri Sep 28, 2018 12:29 am

### Re: 7th edition 4F.11

The question is,

"During the test of an internal combustion engine, 3.00 L of nitrogen gas at 18.5°C was compressed suddenly (and irreversibly) to 0.500 L by driving in a piston. In the process, the temperature of the gas increased to 28.1°C. Assume ideal behavior. What is the change in entropy of the gas?".

The answer key shows using the formula: deltaS = nRln(T2/T1), rather than: deltaS = n(R*5/2)ln(T2/T1). Is this a viable formula?

chloewinnett1L
Posts: 55
Joined: Fri Sep 28, 2018 12:20 am

### Re: 7th edition 4F.11

Still have this question. Is it possible to use R instead of C when calculating the entropy of reversible isobaric compression due to change in temperature, as the solution manual says?

tierra parker 1J
Posts: 61
Joined: Fri Sep 28, 2018 12:17 am

### Re: 7th edition 4F.11

is it because the pressure is also changing that you can't use the nCln(T2/T1) equation?