Constant Pressure and Volume


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

Constant Pressure and Volume

Postby Sarah Sharma 2J » Tue Feb 13, 2018 11:24 am

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?"

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Re: Constant Pressure and Volume

Postby Chem_Mod » Tue Feb 13, 2018 4:52 pm

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.

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