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

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

The reaction quotient \( Q_c \) is defined as:

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

Substituting the given concentrations yields:

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

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

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

A comparison shows that \( Q_c = 1 \) is greater than \( K_c = 4 \times 10^{-3} \):

$$ Q_c > K_c $$

Step 3: Determine the Reaction Direction

When \( Q_c \) exceeds \( K_c \), the reaction will shift in the reverse direction to reach equilibrium.

This indicates that the equilibrium will shift to the left, favoring the backward reaction.

Step 4: Conclusion

The conclusion is: Option (3): The reaction tends to proceed in the backward direction.