Affect of Changing Pressure on K

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Ayesha Aslam-Mir 3C
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Affect of Changing Pressure on K

Postby Ayesha Aslam-Mir 3C » Tue Jan 12, 2021 12:08 am

I understand that adding an inert gas to alter pressure of a rxn of gases would not change Kc and therefore by Le Chatelier's the reaction would not change/respond. What about Kp though?

Pranav Kadiyala 1A
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Re: Affect of Changing Pressure on K

Postby Pranav Kadiyala 1A » Tue Jan 12, 2021 12:16 am

I'm not 100% sure, but I can make an inference:

Given that it is an inert gas, it would be on the products and reactant side. It's partial pressure would also not change, because nothing is really happening to it. Thus, in the equilibrium constant equation it would just cancel out. Accordingly, Kp wouldn't change.

Hope this helps :)

Andrew Jubintoro 3J
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Re: Affect of Changing Pressure on K

Postby Andrew Jubintoro 3J » Tue Jan 12, 2021 7:11 am

To add on to the answer above, you might think that adding more gases into the system/container will increase the pressure inside the container. You then will be right but remember that we are only concerned about the Partial pressures of the substances involved in the equilibrium reaction. So while the total pressure of the system increases, the total pressure does not have any effect on the equilibrium constant.

Lauren To 1E
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Re: Affect of Changing Pressure on K

Postby Lauren To 1E » Tue Jan 12, 2021 7:45 pm

I don't think Kp would change in this case either because it's just another way of expressing the equilibrium constant. Even if the total pressure of the system changes, the partial pressures of the reactants and products would still have the same ratio so Kp would stay the same. You can think of Kc and Kp as being the same since they both represent the equilibrium constant, just in different units. This is also the reason we can convert Kp to Kc and vice versa using the ideal gas law.

Tracey Huynh 2F
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Re: Affect of Changing Pressure on K

Postby Tracey Huynh 2F » Tue Jan 12, 2021 10:06 pm

Hi! I agree with the above answers. Since the equilibrium constant K can be expressed as either Kc or Kp, both "versions" of K would remain constant under changes in concentration or pressure (if it doesn't affect the volume). Even if an inert gas is added to the system, the system will do its best to minimize the change by causing either more reactants (if inert gas was added to products' side) or products (if inter gas was added to reactants' side) to form. As long as the temperature of the system and the volume of the closed environment that the reaction is occurring in remains the same, so does K (Kc or Kp).

Saumya Tawakley 1E
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Re: Affect of Changing Pressure on K

Postby Saumya Tawakley 1E » Tue Jan 12, 2021 10:10 pm

Adding onto previous replies, I think Kp mostly only deals with the partial pressures of gases involved in the reaction. If the partial pressures of the gases in the reaction equation remain unchanged after the addition of a noble gas, then there is consequently no effect on the reaction. Therefore Kp shouldn't change!


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