## using gas constant R

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

Vanessa Reyes_1K
Posts: 60
Joined: Fri Sep 28, 2018 12:28 am

### using gas constant R

For which equations will we use just R versus using 5/2R and 3/2R for an ideal gas?

Zenita Leang 2K
Posts: 67
Joined: Fri Sep 28, 2018 12:28 am

### Re: using gas constant R

You use 3/2R for Cv, when volume is constant in a reaction. This is seen in deltaS=nClnT2/T1. You use 5/2R for Cp when pressure is constant in a reaction, this could be used in the same equation.

Brian Chhoy 4I
Posts: 66
Joined: Fri Sep 28, 2018 12:16 am

### Re: using gas constant R

I dont think R is ever used as a C value in the entropy equation as temperature changes. The C value also changes depending on the shape od the molecule. Th R value by itself would mostly be used in the work equation for reversible work.

Bruce Chen 2H
Posts: 60
Joined: Fri Sep 28, 2018 12:26 am

### Re: using gas constant R

You use 3/2R for when volume is constant and then 5/2R and 3R depending on the type or molecule. You use 5/2R when pressure is constant and then 7/2R and 4R for each subsequent shape.

ran2000
Posts: 66
Joined: Fri Sep 28, 2018 12:15 am

### Re: using gas constant R

5/2 R= C when the pressure is constant
3/2 R= C when the volume is constant

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