## Constant Pressure and Volume

$w=-P\Delta V$
and
$w=-\int_{V_{1}}^{V_{2}}PdV=-nRTln\frac{V_{2}}{V_{1}}$

Sarah Sharma 2J
Posts: 33
Joined: Fri Sep 29, 2017 7:05 am

### Constant Pressure and Volume

When calculating for entropy, when will we know when to implement 5/3 R and 3/2 R for an expression? Are there any hints in the equation other than "at constant pressure/volume?"

Chem_Mod
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Joined: Thu Aug 04, 2011 1:53 pm
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### Re: Constant Pressure and Volume

Hi, Sarah,
3/2 R is a molar heat capacity at constant volume, while 5/2 R is at constant pressure. Whenever, in the question, the volume or pressure is not changing, you can use 3/2R or 5/2 for C respectively. Just check if there is any information whether the pressure is changed. If not, use 5/2R. Same for volume.