Inert Gases and Equilibrium Constant

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Areena H 2K
Posts: 81
Joined: Wed Dec 05, 2018 12:18 am

Inert Gases and Equilibrium Constant

Postby Areena H 2K » Sun Jan 12, 2020 4:23 pm

Why does removing or adding an inert gas in a chemical equation not change the equilibrium constant?
Adding or removing an inert gas affects the pressure and physical parameters based on La Chatalier's Principle since physical parameters cause a shift in the reaction, so why do we say that inert gases don't cause a shift?

Alice Chang 2H
Posts: 101
Joined: Fri Aug 30, 2019 12:18 am

Re: Inert Gases and Equilibrium Constant

Postby Alice Chang 2H » Sun Jan 12, 2020 4:30 pm

I thought this site helped a bit to explain: https://chemistry.stackexchange.com/questions/18567/what-would-be-the-effect-of-the-addition-of-an-inert-gas-to-a-reaction-at-equili

Basically, inert gasses only affect equilibrium if the volume changes.

Hussain Chharawalla 1G
Posts: 100
Joined: Sat Jul 20, 2019 12:15 am

Re: Inert Gases and Equilibrium Constant

Postby Hussain Chharawalla 1G » Sun Jan 12, 2020 4:38 pm

I believe that's the point Dr. Lavelle was trying to make with that demonstration. Pressure itself does not change the reaction quotient. Rather, the change in concentration of the reactants is what affects the reaction quotient.

When you add an inert gas, you are increasing the pressure in the container. But the concentration of your reactants is not changing (you still have the same number of reactant moles of gas in a fixed volume). So pressure is not the driving factor with La Chatalier's principle. But when you decrease the volume of the container you now have more moles of reactant per volume and now are increasing the concentration of reactant gas in the chamber. This is what causes a shift in the equilibrium

005324438
Posts: 51
Joined: Sat Aug 24, 2019 12:16 am

Re: Inert Gases and Equilibrium Constant

Postby 005324438 » Sun Jan 12, 2020 4:42 pm

Pressure alone doesn't change the equilibrium constant. The reason there is a change when we "increase pressure" is actually due to the decrease in volume, and change in concentrations of those initial gases. Adding an inert gas that will have no effect on the reaction doesn't change the equilibrium concentrations because there is no change in initial concentration.

AGaeta_2C
Posts: 112
Joined: Wed Sep 18, 2019 12:21 am

Re: Inert Gases and Equilibrium Constant

Postby AGaeta_2C » Sun Jan 12, 2020 7:35 pm

I was confused on this, too. Is this thinking correct?:

Because the equilibrium constant is a ratio of product concentration (moles/volume) to reactant concentration at equilibrium, it is unaffected by increases in pressure (by adding an inert gas) as long as the volume stays the same.

Thank you:)


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