# Entropy in an isobar transformation

## Main Question or Discussion Point

What is the variation of entropy in an isobar transformation?

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Andrew Mason
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What is the variation of entropy in an isobar transformation?
Are we dealing with an ideal gas? If so, we can work it out from: TdS = dU + PdV

If P is constant then:

$\Delta S = \int \frac{dU}{T} + P\int \frac{dV}{T}$

If this is an ideal gas where PV = nRT, then we can substitute nRT/V for P (or nRdT/P for dV) and nCvdT for dU. Can you work that out?

AM

Yes, it's just so!
Thank you very much! :)