Changes in Pressure

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

605168557
Posts: 65
Joined: Fri Sep 28, 2018 12:18 am

Changes in Pressure

Why is the ratio (P1/P2) in the equation deltaS=nRln(P1/P2) instead of (P2/P1) like with the case of changing volume and changing temperature?

Felicia1E
Posts: 31
Joined: Fri Sep 28, 2018 12:22 am

Re: Changes in Pressure

It has to do with the equation PV=nRT. P and V are inversely related, so in the formula, you would also have to make sure your terms are inverses. It should be that if you have P1 corresponding to V1 and a P2 corresponding to a V2, which you can find one by the other through PV=nRT, deltaS=nRln(P1/P2) will yield you the same answer as deltaS=nRln(T2/T1).

Sarah Kiamanesh 1D
Posts: 30
Joined: Fri Sep 28, 2018 12:22 am

Re: Changes in Pressure

as given by Boyle's law, P1V1=P2V2. If you divide the P2 over to the left and the V1 over to the right, the relation becomes
P1/P2 = V2/V1. The left side of the equation is therefore interchangeable with the ratio on the right

Riley Dean 2D
Posts: 60
Joined: Fri Sep 28, 2018 12:15 am

Re: Changes in Pressure

Because the equation P1V1=P2V2 is true, you can manipulate it so P1/P2=V2/V1

Posts: 57
Joined: Fri Sep 28, 2018 12:27 am

Re: Changes in Pressure

This is tied back to the equation PV=nRT. Due to 'P' and 'V' being multiplied together, they are inversely proportional. When volume goes up, pressure goes down and vice versa.

Ashe Chen 2C
Posts: 31
Joined: Mon Jan 07, 2019 8:23 am

Re: Changes in Pressure

because of the ideal gas law, pressure and volume have an inverse relationship and thus when volume increases, pressure decreases.