## 9.13 6th edition

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

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### 9.13 6th edition

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?

I know that for this problem we have to calculate the entropy separately and then add them, but for the changing volumes how are we suppose to know what number of moles to use?