What is the equilibrium constant expression (K) for the reaction: CO2(g) + H2(g) ⇌ CO(g) + H2O(l)?

• A. K = [CO][H2] / [CO2][H2O]
• B. K = [CO] / [CO2][H2]
• C. K = [CO][H2O] / [CO2][H2]
• D. K = [CO][H2O] / [CO2]

Answer: (B)

Verified step by step guidance

1. Identify the balanced chemical equation: \( \mathrm{CO_2(g)} + \mathrm{H_2(g)} \rightleftharpoons \mathrm{CO(g)} + \mathrm{H_2O(l)} \).
2. Recall that the equilibrium constant expression \( K \) is written in terms of the concentrations of the products over the reactants, each raised to the power of their stoichiometric coefficients.
3. Write the general form of the equilibrium constant expression: \[ K = \frac{[\text{products}]}{[\text{reactants}]} = \frac{[\mathrm{CO}]^{1} [\mathrm{H_2O}]^{1}}{[\mathrm{CO_2}]^{1} [\mathrm{H_2}]^{1}} \].
4. Recognize that since \( \mathrm{H_2O} \) is a liquid, its concentration is essentially constant and is omitted from the equilibrium expression.
5. Therefore, simplify the expression to: \[ K = \frac{[\mathrm{CO}]}{[\mathrm{CO_2}][\mathrm{H_2}]} \].