Midterm 1 Question 2

[106268412]

Can someone explain how they reached the correct answer for number 2 on Midterm 1. I thought that when there is an increase in pressure, equilibrium would shift toward the side where there is less moles of gas. So, why would it not favor product formation in this case?

[Yifan_Wang_2A]

In this question, the pressure is increased due to the addition of helium gas which is irrelevant to the gases in the reaction. If the pressure is increased due to the decrease in volume, then the equilibrium will shift to the side with fewer moles.

[106268412]

Doesn't the left side have more moles of gas though, and the right side as fewer moles of gas. So, wouldn't that favor product formation (aka. the right side)? The answer is false, right?

[grace thomas 1D]

An easier way to think about it is that helium is an inert gas, and increasing pressure by pumping an inert gas does not affect the reaction as the moles of reactant and product along the volume stays constant.

[Sono Fukushima 2D]

Then why for question 3 does the volume change affect it? I don't understand why adding helium in question 2, while not changing the mols of reactant or product, wouldn't decrease the volume available for the reaction to occur, which would be an increase in pressure?? Still confused on this one.