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Topic: Heat of formations and vapour pressure  (Read 3714 times)

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Offline realdon

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Heat of formations and vapour pressure
« on: February 09, 2008, 11:20:48 PM »
The standard free energy of formation for liquid ethanol is -174.9 kJ/mol and that for gaseous ethanol is -168.6 kJ/mol. Calculate the vapour pressure of ethanol at 25C, in mmHg.

I really don't know how the energy of formations and vapour pressure are related. Thanks a lot.
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Offline Yggdrasil

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Re: Heat of formations and vapour pressure
« Reply #1 on: February 10, 2008, 12:18:24 AM »
hint: you can think of the vapor pressure as an equilibrium constant
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Offline realdon

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Re: Heat of formations and vapour pressure
« Reply #2 on: February 10, 2008, 12:50:00 AM »
But isn't the heat of formation enthalpy? G=-RTlnK only works with Gibb's free energy
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Offline Yggdrasil

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Re: Heat of formations and vapour pressure
« Reply #3 on: February 10, 2008, 12:57:08 AM »
Yes, heat of formation is a change in enthalpy.  But you stated that you were given the free energies of formation
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Offline realdon

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Re: Heat of formations and vapour pressure
« Reply #4 on: February 10, 2008, 04:15:43 PM »
Srry, I misread that part

Thanks for correcting me
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