Affect of Changing Pressure on K

[Ayesha Aslam-Mir 3C]

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]

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]

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]

I don't think K_p 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 K_p would stay the same. You can think of K_c and K_p as being the same since they both represent the equilibrium constant, just in different units. This is also the reason we can convert K_p to K_c and vice versa using the ideal gas law.

[Tracey Huynh 2F]

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]

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!