## Pistons and Reversibility

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

Payton Kammerer 2B
Posts: 49
Joined: Tue May 01, 2018 3:00 am

### Pistons and Reversibility

In the sixth edition of the textbook, one of the practice problems describes a situation in which a gas is compressed with a piston, but says that this compression is irreversible, and asks to calculate the entropy. This question confuses me for two different reasons, 1) isn't entropy a state function, so the reversibility shouldn't be relevant? and 2) isn't the whole point of a piston that the compression is reversible?

Thanks!

Chem_Mod
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### Re: Pistons and Reversibility

1. Yes, you are correct. Entropy is a state function so it does not matter whether it is reversible or irreversible
2. Not necessarily; pistons you might use in daily life, sort of like syringes for example, do not compress reversibly