Why don't inert gases affect equilibrium?

[Labminion]

I have read that the addition of an inert gas to an equilibrium reaction held at a constant volume exerts no effect on the equilibrium. I would think that by adding another gas (i.e., to a mixture of gases), even if it is inert and non-reactive, would increase the overall pressure of the system. An increase in the system's pressure would then cause the equilibrium to shift in the direction with fewer gas molecules (assuming there are unequal numbers of molecules on each side of the reaction). Can somebody clear this up for me?

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[LeonVCU]

A gas will affect the equilibrium if it participating in the equilibrium reaction. A + B --> C + D. So, if you increase D, the reaction will go to the left, producing more reactants. If you add E (an inert gas, any letter other than A, B, C, and D), you will not change the equilibrium

 

[MT Headed]

Here's another way to think of it. By adding an inert gas you increased the total gas pressure of the system, but you didn't change the partial gas pressure of any reactants/products.

So when you go plugging in partial pressures into your Kp = (products)/(reactants) equation, well, you are putting in the same numbers.

 

[imapremed]

I have read that the addition of an inert gas to an equilibrium reaction held at a constant volume exerts no effect on the equilibrium. I would think that by adding another gas (i.e., to a mixture of gases), even if it is inert and non-reactive, would increase the overall pressure of the system. An increase in the system's pressure would then cause the equilibrium to shift in the direction with fewer gas molecules (assuming there are unequal numbers of molecules on each side of the reaction). Can somebody clear this up for me?

wow dude thanks for asking this... i never knew this myself until i looked it up http://en.wikipedia.org/wiki/Le_Chatelier's_principle#Effect_of_adding_an_inert_gas ...

what if this actually pops up on my mcat. i will love you forever no homo.