## Calculating Entropy of Surroundings

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

Isaac_Partida_1F
Posts: 10
Joined: Sat Jul 09, 2016 3:00 am

### Calculating Entropy of Surroundings

I was trying to to do Self-Test 9.15A in the book which says "Calculate the entropy change of the surroundings when 1.00 mol H2O(l) vaporizes at 90 degrees C and 1 bar." The question continues but I couldn't get over this first part. How does water vaporize at 90 degrees C if the boiling point is 100 degrees C?

stephanieyang_3F
Posts: 62
Joined: Wed Sep 21, 2016 2:55 pm

### Re: Calculating Entropy of Surroundings

This question is similar to a question that was discussed in some discussions regarding 9.19 in the problem set. You need to calculate the entropy change to raise that liquid water to 100 C, then calculate the entropy change for the phase change, and finally calculate the entropy change for the cooling of water vapor back to 90 C. You add those change in entropies to find the total entropy of this problem. The only part I'm not sure about is the entropy change of the "surroundings"... but this is definitely how to calculate the entropy of change of 1.00 mol H2O(l) vaporizes at 90 degrees C and 1 bar.