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Vapor pressure

  • Thread starter rxrocky
  • Start date
3
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Hello everyone!

I've encountered a small problem with one of our "special" assignments.

Question:
The normal boiling point for ethyl alcohol is 78.4 C, S for C2H5OH(g) is 282,7 J/mol*K.
At what temperature is the vapor pressure of ethyl alcohol 357 mm Hg?

Maybe I'm stupid, but I can't find a connection between the pressure and entropy. Or the phase transition. Original I thought it had something to do with Gibbs vs equilibrium, but now I'm even more confused.

I'd love to do the problem myself but I'm in need of a hint/tip :)

Thanks in advance.
 

Answers and Replies

GCT
Science Advisor
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The only equation that comes to mind at the moment is some type of derivative of the Clayperon equation.
 
Mapes
Science Advisor
Homework Helper
Gold Member
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Yes, this is definitely a Clapeyron relation problem. The change in characteristic pressure of a phase transformation with temperature is related to the enthalpy of the transformation. And the enthalpy change is related to the entropy change. Let us know if you get stuck.
 
3
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Thanks for the help.

I'll post my calculations later today, still not entirley sure I got it right.
 

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