## Chapter 9, Question 7

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

Jesus Rodriguez 1J
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Joined: Sat Jul 22, 2017 3:00 am

### Chapter 9, Question 7

Can someone explain to me why we had to multiply the gas constant by 5/2 and 3/2?

Shane Simon 2K
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Joined: Fri Sep 29, 2017 7:05 am

### Re: Chapter 9, Question 7

When a monatomic ideal gas is at constant pressure, the R constant is multiplied by 5/2. When a monatomic ideal gas is at constant volume, it is multiplied by 3/2. I do not believe we need to know where these numbers came from just that we need to use them in these situations of constant pressure or volume with ideal gases. I remember Professor Lavelle saying something about there being a 1/2 value for each axis of a 3-dimensional graph and adding those all together gave the 3/2 number but he said we didn't need to know any specifics.

Sabah Islam 1G
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Joined: Sat Jul 22, 2017 3:01 am

### Re: Chapter 9, Question 7

Both molar heat capacities (Cp= 5/2R and Cv=3/2R) are given constants that can be found on the Constants and Equations sheet that is found on Dr. Lavelle's website and given to us during tests. Also, the R in both constants is the gas constant 8.314 JK^-1mol^-1. For an ideal gas at constant pressure, you would use 5/2 and for an ideal gas at constant volume, you would use 3/2.