An amount of 1 mole each of A and D is introduced in 1L container. Simultaneously the following two equilibria are established:
A ⇌ B + C; K_c = 10⁶ M² and
B + D ⇌ A; K_c = 10⁻⁶ M⁻¹
The equil

Question

An amount of 1 mole each of A and D is introduced in 1L container. Simultaneously the following two equilibria are established:
A ⇌ B + C; K_c = 10⁶ M² and
B + D ⇌ A; K_c = 10⁻⁶ M⁻¹
The equilibrium concentration of A will be

Prashant Kotian · Accepted Answer

Correct answer: A. Due to large K_c for A ⇌ B + C, almost all 1M of A decomposes to 1M B and 1M C. The second reaction B + D ⇌ A has very small K_c, meaning it stays mostly as B + D. Thus [B] ≈ 1, [C] ≈ 1, [D] ≈ 1. Using K_c for A ⇌ B + C, [A] = [B][C] / K_c = (1 × 1) / 10⁶ = 10⁻⁶ M. Therefore, correct answer is A.

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