For the reaction: A + B ⇌ C + D, the initial concentration of A and B is equal, but the equilibrium — Chemical Equilibrium Chemistry Question

💡 Solution & Explanation

Let initial [A] = [B] = a. Let x react. Eq [A] = a-x, [B] = a-x, [C] = x, [D] = x. Given [C] = 2[A], so x = 2(a-x) => x = 2a - 2x => 3x = 2a => x = 2a/3. Eq concentrations: [C] = [D] = 2a/3, [A] = [B] = a/3. K_c = ([C][D]) / ([A][B]) = (2a/3 × 2a/3) / (a/3 × a/3) = 4. Therefore, correct answer is A.