The value of the equilibrium constant at a given temperature

The value of the equilibrium constant at a given temperature for the reaction:

2HI(g) <---> H2(g) + I2(g)

is 0.200. If [HI] = 0.200 M, [H2] = 0.200 M, and [I2] = 0.200 M, determine if the reaction is at equilibrium. If it is not, in which direction will proceed to reach equilibrium?

A. To reach equilibrium, the value of Keq must change.

B. It is not possible to tell if the reaction is at equilibrium.

C. The reaction is not at equilibrium.

D. The reaction is not at equilibrium, it will shift to the left.

E. The reaction is not at equilibrium, it will shift to the right.

Please explain how you found your answer.

Solution

Q = [H2][I2]^2/[HI]^2 = (0.2x0.2)/(0.2)^2 = 1,

K = 0.2, hence K < Q

hence reaction is not at equilibrium. it shifts towards left so that Q decreases untill it becomes value of K.

hence answer is D