joniaguis - 2-5-2009 at 13:38
I need some assistance over the following question. I don't know exactly which equation I have to use.
Determine the entropy change when one mole of a liquid (bpt 356K) is heated from 298K up to 428K given the following information:
Cp of liquid: 45 cal/mole/degree
Cp of vapour: 10.8 + 3.35 x 10^-2 T + 0.95 x 10^-4 T^2 cal/mole/degree
heat of vapourisation: 4405 cal/mole
JohnWW - 2-5-2009 at 18:02
This question really belongs in the "Beginnings" section. A clue: You can fairly readily calculate the enthalpy change at constant pressure, by adding
the heat of vaporization to the increase in heat content on heating the liquid to the boiling point by multiplying the Cp (liquid) by the temperature
change, and to the subsequent increase in heat content of the vapor by integrating the formula for the Cp (vapor) from the b.pt. up to the final
temperature. Then you can apply the Gibbs equation:
(delta)G = (delta)H - T.(delta)S, where (delta)S is the change in entropy, (delta)G is the change in Gibbs free energy, and (delta)H is the change in
enthalpy. See also Perry chapter 4.
DJF90 - 2-5-2009 at 19:38
I've taken the liberty of providing a worked answer. Hopefully you have a decent understanding of calculus and thermodynamics in general.
Attachment: Entropy Solution.pdf (35kB)
This file has been downloaded 495 times
joniaguis - 3-5-2009 at 00:11
I tried it yesterday and Ive got 26.81cal/mol as answer. I try to analyze the question and see where I could have gone wrong.
joniaguis - 3-5-2009 at 00:27
found the mistake. Thanks a lot mate.
Nicodem - 4-5-2009 at 00:07
I have no idea what this thread was doing in the Energetic Materials section. Moved to Beginnings section...
DJF90 - 5-5-2009 at 00:02
No problem. My solution is correct yes? That is very encouraging especially as I have exams in 5 weeks...
joniaguis - 5-5-2009 at 03:58
same here exams too. That was a past paper question. good luck with yours.