## 7th edition 4F.11

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

paytonm1H
Posts: 74
Joined: Fri Sep 28, 2018 12:18 am

### 7th edition 4F.11

In this question, it asks you to calculate net change in entropy for a change in volume and temperature, but you aren't given the moles of gas. It tells you to assume ideal behavior (P=1.00atm), and the answer key also says to assume 1 mol of gas. Is this always true for gas at ideal behavior?

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

Hello, can you please post the full text of the question from the book for better reference?

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

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

The full 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). Can we use this formula?

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

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

i don't think you can use that equation with the 5/2R because the pressure isn't constant. since it's a compression if volume decrease then pressure increases

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