Question

What happens to the following reaction at equilibrium if the pressure is decreased?
2H2(g) + O2(g) 2H2O(g)


A. The equilibrium shifts left because Q > K.
B. The equilibrium shifts right because Q < K.
C. The equilibrium shifts left because Q < K.
D. The equilibrium shifts right because Q > K.

I have already ruled out answer C but I'm not sure which one it is. Can someone help me please?

Answer 1

Please explain how you eliminated answer C.
The rule with gases is that an INCREASE in P makes the reaction shift to the side with FEWER mols which means an increase in P and the reaction shifts to the right in this reaction (2 mols on right; 3 mols on left). It follows that a decrease in P makes it shift to the left.
Q = Keq at equilibrium = (H2O^)^2/(H2)^2(O2). Why does it shift to the left? Because H2O is too large and H2 and O2 are too small. Therefore, A or C.

Answer 2

A for apex