# Entropy in an isobar transformation

1. Jul 13, 2012

### alialice

What is the variation of entropy in an isobar transformation?

2. Jul 13, 2012

### Andrew Mason

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

3. Jul 13, 2012

### alialice

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