## 6th edition 9.19

Christina Chang 1C
Posts: 34
Joined: Thu May 10, 2018 3:00 am

### 6th edition 9.19

I was not sure how to do this problem, but the solutions guide said to calculate the heat and the phase change and then to calculate the heat of going back too. Why would you have to go back after the phase change?

Kassidy Tran 1E
Posts: 77
Joined: Fri Sep 28, 2018 12:15 am

### Re: 6th edition 9.19

The system starts at 85C, and since you are given the standard enthalpy at 100C, you have to use 3 different types of deltaS in this problem: the change in entropy when you go from 85C to 100C, the deltaS at 100C, and then the deltaS when you go from 100C to 85C. You have to go through all these steps because you’re not given the standard entropy vaporization at 85C, but 100C.

Alysa Rallistan 2G
Posts: 32
Joined: Thu Jan 17, 2019 12:16 am

### Re: 6th edition 9.19

You use these 3 different steps because we are not given standard entropy of vaporization at 85C, this is essentially making a loop, you heat the substance to 100 and calculate the entropy then while T =100C meaning it remains constant, then you calculate the change in entropy there, and finally you cool the substance back down to 85C and calculate the change in entropy for that. Finally you add all the individual values for the change in entropy to give you the overall change in entropy