Joe’s Review Session

Volume: $\Delta S = nR\ln \frac{V_{2}}{V_{1}}$
Temperature: $\Delta S = nC\ln \frac{T_{2}}{T_{1}}$

Kellina Tran 2I
Posts: 50
Joined: Sat Jul 22, 2017 3:00 am

Joe’s Review Session

For anyone who went to Joe’s review session today, can someone give me a run-through on the steps to solve the problem he gave us with calculating the total deltaS for vaporization of C2H5OH, including the numbers you got for each step? I keep getting the wrong answer and I’m not sure why. I believe the answer was around 130 J.K^-1.mol^-1.

Justin Chang 2K
Posts: 53
Joined: Fri Sep 29, 2017 7:04 am

Re: Joe’s Review Session

yes, here is the problem!

Ethanol: what is the entropy of vaporization of 1 mol of ethanol at 285K?
C(l)=111J/Kmol
C(g)=78.3J/Kmol
B.P=351.5K
deltaHvap=43.5kJ/mol
1) deltaS=n*C(l)*ln(351.5/285)= 23.28J/K
2) deltaS=(43500J/mol) / 351.5= 123.755J/K
3) deltaS=n*C(g)*ln(285/351.5)= -16.42J/K

deltaStotal=130.6J/K