7th ed. 4I9

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

Emmaraf 1K
Posts: 94
Joined: Sat Oct 20, 2018 12:16 am

7th ed. 4I9

For part b, you are asked to find S of surroundings, system, and total for an irreversible isothermal expansion. In the solution, it says w=0 since it's a free expansion (what does this mean?) and that delta U=0 (but why if it is irreversible?). It later says delta S surroundings = 0 and total entropy change is delta S of the system. Can anyone explain how this is derived?

Elisa Bass 4L
Posts: 61
Joined: Fri Sep 28, 2018 12:23 am

Re: 7th ed. 4I9

No work is done in free expansion because there is no pressure against which the gas expands and does work. But you don’t need to figure out IF it’s free expansion because the problem will always indicate this, as this one has.

Mindy Kim 4C
Posts: 65
Joined: Fri Sep 28, 2018 12:25 am

Re: 7th ed. 4I9

I believe deltaS of the surroundings is zero because even if there is a small change in entropy in the surroundings, your surroundings are so large that such a change would essentially be insignificant and there would be almost no change.