For the reaction 2A(g) + B(g) ⇌ 2C(g), the equilibrium constant Kc is 2.0 at a certain temperature. If the equilibrium concentrations are [A] = 0.40 M and [B] = 0.20 M, what is the equilibrium concentration of C?
Show the answer and explanation
Correct answer
C. 0.25 M
Principle or equation
For a reaction aA + bB ⇌ cC, the equilibrium constant expression is Kc = [C]^c / ([A]^a [B]^b). Solve for [C] using the given concentrations.
Why this answer is correct
Kc = [C]^2 / ([A]^2 [B]) = 2.0. Substitute [A] = 0.40 and [B] = 0.20: 2.0 = [C]^2 / (0.40^2 × 0.20) = [C]^2 / (0.16 × 0.20) = [C]^2 / 0.032. Thus [C]^2 = 2.0 × 0.032 = 0.064, so [C] = sqrt(0.064) = 0.25 M.
Example
If Kc = 4.0 for A + B ⇌ C with [A]=0.10, [B]=0.10, then [C] = 4.0 × 0.10 × 0.10 = 0.040 M.
This published item includes a stored explanation and passed the platform’s publication workflow. It is independent preparation material, not a claim of an official or recalled examination question.