## 9.85

$\Delta S = \frac{q_{rev}}{T}$

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Joined: Fri Sep 29, 2017 7:05 am

### 9.85

For part c and d of this question, how do we know whether positional or thermal disorder is dominant? I know that in d, the solution manual says that the surroundings participate in the solution process only as a source of heat, so the entropy change of the surroundings is primarily a result of the dispersal of thermal motion, but how do we know that?

Kelly Kiremidjian 1C
Posts: 62
Joined: Fri Sep 29, 2017 7:04 am

### Re: 9.85

For part C, it asks if the entropy of the system is primarily a result of changes in positional disorder or thermal disorder. The system here is the solution, so if you imagine potassium nitrate dissolving in water it makes logical sense that the entropy, or disorder of the system is mostly the potassium nitrate dispersing in the water.

Part D, however, asks for the entropy changes of the surroundings to the solution. Around the cup or beaker where the solution is in is not experiencing any positional disorder like the potassium nitrate dissolving, the dominant entropy change of the surroundings is thermal disorder, like the surroundings gaining heat from the system.

Hope this helps