2003 AIPMT EquilibriumReaction Quotient and Direction of Reaction Easy Question 90 of 104 in Equilibrium

The reaction quotient (Q) for the reaction : $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$ is given by $Q = \dfrac{[NH_3]^2}{[N_2][H_2]^3}$. The reaction will proceed from right to left if : (where $K_C$ is the equilibrium constant)

A $Q = K_C$
B $Q \lt K_C$
C $Q \gt K_C$
D $Q = 0$

The answer is C.

Solution

The reaction quotient Q has the same form as $K_C$ but uses the concentrations at any moment.
If $Q \lt K_C$: products are less than at equilibrium, so the reaction goes forward (left to right).
If $Q = K_C$: the system is at equilibrium.
If $Q \gt K_C$: there is too much product ($NH_3$) compared with equilibrium, so the reaction goes backward, from right to left, until Q falls to $K_C$.
So the reaction proceeds from right to left if $Q \gt K_C$.

Concept Comparing Q with K

Equilibrium in past papers

104 questions from this chapter have appeared across 27 exam years.