[YourWorstNightmare]

Okay, my understanding of gas equilibrium systems is that if a given system is at equilibrium, and then you increase the pressure the equilibrium will shift in the direction that has fewer gas molecules (which makes complete sense to me), and vice versa.

When given the equilibrium system as follows:

Methane (g) + Water (g) + 20.50 kJ  Carbon Monoxide (g) + 3 Hydrogen (g)

And told that the pressure was increased by adding an inert gas, since there was 4 gas molecules on the right side and 2 on the left I assumed that the reaction would then shift in the left direction and that [CO] would decrease.  However, I wrote that on a test and it was incorrect.

I figured I should get to the bottom of it before I saw the exact same question on the exam.

[Borek]

Equilibrium depends on the partial pressures of gases. When you add an inert gas total pressure changes, but partial pressures of the compounds involved in the equilibrium do not.