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Practice Midterm from Sunday's Review Sess - #3C

Posted: Sun Feb 11, 2018 8:48 pm
by Joshua Hughes 1L
the problem was: True/False: One cannot calculate the entropy of vaporization for water at room temperature because water has a boiling point of 373K.
The answer was False. Can someone please help explain this to me because I didn't understand the bit in the session. He started setting up a calculation and I got kind of lost. I am confused because it's not like you are heating the water to 373K to vaporize/boil it. I know water evaporates even below 373K but he split the calculation into three parts and I was just hoping someone could explain it to me. Thank you.

Re: Practice Midterm from Sunday's Review Sess - #3C

Posted: Sun Feb 11, 2018 9:06 pm
by Mitch Mologne 1A
You can still calculate it by taking values and equations you know already. Because deltaS is a state function, you can take multiple steps to get there rather than just one. Just because water is not boiling at room temp, you can still find it the entropy of vaporization.

Re: Practice Midterm from Sunday's Review Sess - #3C

Posted: Sun Feb 11, 2018 9:14 pm
by Chem_Mod
Hi Joshua,
The concept I was trying to explain is that as long as you arrive at the same final state/condition, you can create any path with any steps and add up the entropy changes for all of them. This is because entropy is a state function, and is path independent. For further clarification, feel free to drop into Hedrick from 5-7pm tomorrow, 2/12 where I will be covering for Michael's UA session,

Re: Practice Midterm from Sunday's Review Sess - #3C

Posted: Sun Feb 11, 2018 9:30 pm
by ZoeHahn1J
We can calculate the entropy of vaporization of water at a temperature lower than its boiling point by adding delta S due to increasing the temperature to the boiling point + entropy of vaporization of water at the boiling point + delta S due to decreasing the temperature of the water back to the original temperature. We can do this because entropy is a state function.