Textbook Problem 4F.17

[005917072]

This question asks to calculate the standard entropy of vaporization of water at 85 C, and I wasn't sure how to solve it so I checked the solutions manual but I don't get the explanation either? It says there's three steps, each of which you add the entropy of, and I understand why the first step is the finding entropy of raising the temperature to 100 C and then second is the entropy of vaporization, but then it says the third step is the entropy of cooling the products back to 85 C, and I don't really understand why that third step is done?

[Ryan Mostafavi 1C]

You have to do the third step because it at 85 C therefore the final temp must be 85 C.