Boiling Point Mystery for Ethyl Alcohol

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Discussion Overview

The discussion revolves around a problem related to the boiling point of ethyl alcohol, specifically exploring the relationship between vapor pressure, temperature, and entropy. Participants are examining the application of thermodynamic principles, particularly the Clapeyron equation, in solving the problem.

Discussion Character

  • Homework-related, Technical explanation, Exploratory

Main Points Raised

  • One participant expresses confusion about the connection between pressure, entropy, and phase transitions, initially considering Gibbs free energy but feeling uncertain.
  • Another participant suggests that the problem relates to the Clapeyron equation, indicating that the change in pressure during a phase transformation is linked to the enthalpy and entropy changes.
  • A third participant confirms the relevance of the Clapeyron relation and encourages the original poster to share their calculations for further assistance.

Areas of Agreement / Disagreement

Participants generally agree that the Clapeyron equation is applicable to the problem, but there is no consensus on the specific calculations or interpretations of the relationships involved.

Contextual Notes

There are unresolved aspects regarding the assumptions made in applying the Clapeyron equation, as well as the specific enthalpy and entropy values needed for calculations.

Who May Find This Useful

This discussion may be useful for students or individuals interested in thermodynamics, particularly those dealing with phase transitions and vapor pressure calculations.

rxrocky
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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.
 
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The only equation that comes to mind at the moment is some type of derivative of the Clayperon equation.
 
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.
 
Thanks for the help.

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

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