## Example 9.5

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

Nha Dang 2I
Posts: 53
Joined: Fri Sep 29, 2017 7:07 am

### Example 9.5

In one experiment, 1.00 mol O2(g) was compressed suddenly (and irreversibly) from 5.00 L to 1.00 L by driving in piston, and in the process its temperature was increased from 20.0 C to 25.2 C. What is the change in entropy of the gas?

In Step 2, why did they use the heat capacity of argon in deltaS=(Cv)ln(T2-T1)?

Lauren Seidl 1D
Posts: 51
Joined: Fri Sep 29, 2017 7:06 am

### Re: Example 9.5

If you look at the bottom of page 325 under the example, it says to assume that argon is an ideal gas, so I am assuming that is why you would use argon's heat capacity.

Nha Dang 2I
Posts: 53
Joined: Fri Sep 29, 2017 7:07 am

### Re: Example 9.5

But why would you use argon when the question is asking about oxygen?

Justin Yu 3H
Posts: 36
Joined: Fri Sep 29, 2017 7:07 am

### Re: Example 9.5

Argon is very very similar to the ideal gas. The molar heat capacity at constant volume for argon is the same as 3/2 R, that of a monoatomic ideal gas. So even though they write argon, you can just interpret that as viewing oxygen as an ideal gas.