Question

For the reaction 2A⇋ B + C, KC = 4 × 10^–3 . At a given time, the composition of reaction mixture is: [A] = [B] = [C] = 2 × 10–3 M. Then, which of the following is correct?

• A. Reaction is at equilibrium.
• B. Reaction has a tendency to go in forward direction.
• C. Reaction has a tendency to go in backward direction.
• D. Reaction has gone to completion in forward direction.

Answer 1

The Correct Option is C

The reaction quotient $Q_c$ is calculated as:
$Q_c = \frac{[B][C]}{[A]^2} = \frac{(2 \times 10^{-3})(2 \times 10^{-3})}{(2 \times 10^{-3})^2} = 1$.
Since $Q_c > K_c$, the reaction will shift in the backward direction to establish equilibrium.

Answer 2

Step 1: Use the Reaction Quotient \( Q_c \) 

The reaction quotient \( Q_c \) is given by:

$$ Q_c = \frac{[B][C]}{[A]^2} $$

Substitute the given concentrations:

$$ Q_c = \frac{(2 \times 10^{-3})(2 \times 10^{-3})}{(2 \times 10^{-3})^2} = \frac{4 \times 10^{-6}}{4 \times 10^{-6}} = 1 $$

Step 2: Compare \( Q_c \) with \( K_c \)

The equilibrium constant \( K_c \) is given as \( 4 \times 10^{-3} \).

Since \( Q_c = 1 \) and \( K_c = 4 \times 10^{-3} \), we see that:

$$ Q_c > K_c $$

Step 3: Direction of the Reaction

When \( Q_c > K_c \), the reaction proceeds in the backward direction to achieve equilibrium.

Therefore, the reaction will shift to the left, and there is a tendency for the reaction to go in the backward direction.

Step 4: Conclusion

The correct answer is:

Option (3): The reaction has a tendency to go in the backward direction.