## Change in vol and temp

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

manasa933
Posts: 72
Joined: Fri Sep 29, 2017 7:04 am

### Change in vol and temp

What formula (for entropy) do we use if there is a change in both volume and temperature?

Naomi Jennings 2H
Posts: 21
Joined: Thu Jul 13, 2017 3:00 am

### Re: Change in vol and temp

If there's a change in volume and temperature, you use two different equations, which you can do because Entropy is a state function, so there's the same change whether both volume and temperature change at the same time, or whether volume changes, then temperature. First you can calculate the entropy change at the initial temperature with the change in volume using Delta S =nR (V2/V1). Then you can assume that the temperature changes while the volume remains at the final volume, b using Delta S= Cv(T2/T1).
Then you add the entropy changes from these two steps together to get the total entropy change. Example 9.5 on page 325 in our textbook has an example problem for this.

Yutian Zhao -1J
Posts: 30
Joined: Fri Sep 29, 2017 7:05 am

### Re: Change in vol and temp

You can calculate the entropy change resulting from temp change and volume change together separately and then add them up. Use delta S=nRln(v2/v1) to calculate the detla S for volume change and then use detlaS=nCln(T2/T1) to get the entropy change for temp change.