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### Topic: why does the equilibrium constant changes with temperature and pressure?  (Read 13065 times)

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#### Erik

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##### why does the equilibrium constant changes with temperature and pressure?
« on: August 13, 2012, 06:15:34 AM »
due to le chatalier principle , the system would cause the equilibrium to shift in such a way that it partially removes the disturbance in the system , therefore it causes the increase/decrease in the chemical concentration depending on the side of the equation it is on , the other factor is the enthalpy of the forward and backward reaction, but how to really prove that the increase/decrease would cancel out each other's effect in the change of equilibrium constant ?

#### ramboacid

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##### Re: why does the equilibrium constant changes with temperature and pressure?
« Reply #1 on: August 13, 2012, 01:19:02 PM »
Temperature affects the equilibrium constant, but not pressure. A proof for the non-pressure dependence of the equilbrium constant is on the following page:
http://www.chemguide.co.uk/physical/equilibria/change.html

This explanation however doesn't use thermodynamic considerations but rather examines the calculations behind the equilibrium constant. Hope this helps!
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#### fledarmus

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##### Re: why does the equilibrium constant changes with temperature and pressure?
« Reply #2 on: August 13, 2012, 03:18:50 PM »
The equilibrium constant does not change with pressure, but the equilibrium concentrations of the components will still shift in accordance with Le Chatelier's Principle.

#### Erik

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##### Re: why does the equilibrium constant changes with temperature and pressure?
« Reply #3 on: August 14, 2012, 09:10:17 AM »
ramboacid , do u have a link showing the proof of it by thermodynamic considerations ? help appreciated.

#### ramboacid

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##### Re: why does the equilibrium constant changes with temperature and pressure?
« Reply #4 on: August 14, 2012, 01:29:14 PM »
The best I can come up with is the van't Hoff equation, which relates the natural log of the equilibrium constant inversely to temperature. The equation only refers to temperature and not pressure, so it's a roundabout way of saying pressure doesn't matter I guess... Anyways the link to the wikipedia page is below

http://en.wikipedia.org/wiki/Van_'t_Hoff_equation
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#### curiouscat

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##### Re: why does the equilibrium constant changes with temperature and pressure?
« Reply #5 on: August 21, 2012, 09:43:37 AM »
The best I can come up with is the van't Hoff equation, which relates the natural log of the equilibrium constant inversely to temperature. The equation only refers to temperature and not pressure, so it's a roundabout way of saying pressure doesn't matter I guess..

That's assuming ΔH is independant of P though, right? If ΔH had a P dependence your dK/DT would have a P dependence too?

#### Jorriss

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##### Re: why does the equilibrium constant changes with temperature and pressure?
« Reply #6 on: August 21, 2012, 12:22:31 PM »
The best I can come up with is the van't Hoff equation, which relates the natural log of the equilibrium constant inversely to temperature. The equation only refers to temperature and not pressure, so it's a roundabout way of saying pressure doesn't matter I guess..

That's assuming ΔH is independant of P though, right? If ΔH had a P dependence your dK/DT would have a P dependence too?
The equilibrium constant does technically have a pressure dependence but it's very weak and is neglected generally. One can derive it's pressure dependence as easily as temperature but it's not that important.