## Isothermal pressure change

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

Samantha Joseph 1F
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### Isothermal pressure change

Why is it that the equation for finding the entropy of a system with an isothermal pressure change uses P1/P2 when temperature and volume are typically T2/T1 or V2/V1?

Ju-Wei Wang 1I
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Joined: Fri Sep 29, 2017 7:05 am

### Re: Isothermal pressure change

According to the ideal gas law, specifically Boyle's Law, pressure is inversely related to volume, so at constant temperature, V2/V1=P1/P2.

Matthew 1C
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Joined: Fri Sep 29, 2017 7:06 am

### Re: Isothermal pressure change

I think the reason P1/P2 is used is because it is inversely proportional to volume, which uses V2/V1. Also since both pressure and volume are directly proportional to temperature, does it matter which one uses 1/2 or 2/1?

Ashley Macabasco 2K
Posts: 30
Joined: Fri Sep 29, 2017 7:05 am

### Re: Isothermal pressure change

The change in pressure equation is P1/P2 opposed to P2/P1 like for the change in temperature and the change in volume because of Boyle's law in which volume and pressure are inversely proportional.