What is the equilibrium constant expression (K) for the reaction: CO2(g) + C(s) ⇌ 2 CO(g)?

• A. K = [CO] / [CO2]
• B. K = [CO2] / [CO]^2
• C. K = [CO]^2 / [CO2]
• D. K = [CO]^2 / ([CO2][C])

Answer: (C)

Verified step by step guidance

1. Identify the balanced chemical equation: CO2(g) + C(s) ⇌ 2 CO(g).
2. Write the general form of the equilibrium constant expression for gases and aqueous species: \(K = \frac{\text{products}}{\text{reactants}}\), where each concentration is raised to the power of its stoichiometric coefficient.
3. Recognize that solids (like C(s)) do not appear in the equilibrium expression because their activity is defined as 1 and does not affect the equilibrium.
4. Write the equilibrium constant expression including only gaseous species: \(K = \frac{[\mathrm{CO}]^{2}}{[\mathrm{CO}_{2}]}\).
5. Confirm that the expression excludes the solid carbon and correctly reflects the stoichiometry of the gaseous species.