2.5.2 Test (CST): Computer-Scored Unit Test Question 9 of 21 What is \( K_{\text {eq }} \) for the reaction \( 2 \mathrm{SO}_{3}(g)=2 \mathrm{SO}_{2}(g)+\mathrm{O}_{2}(g) \) ? A. \( \mathrm{K}_{\text {eq }}=\frac{2\left[\mathrm{SO}_{2}\right]\left[\mathrm{O}_{2}\right]}{2\left[\mathrm{SO}_{3}\right]} \) B. \( \mathrm{K}_{\text {eq }}=\frac{\left[\mathrm{SO}_{2}\right]^{2}\left[\mathrm{O}_{2}\right]}{\left[\mathrm{SO}_{3}\right]^{2}} \) C. \( \mathrm{K}_{\text {eq }}=\frac{2\left[\mathrm{SO}_{3}\right]}{2\left[\mathrm{SO}_{2}\right]\left[\mathrm{O}_{2}\right]} \) D. \( K_{\text {eq }}=\frac{\left[\mathrm{SO}_{3}\right]^{2}}{\left[\mathrm{SO}_{2}\right]^{2}\left[\mathrm{O}_{2}\right]} \) SUBM

To derive the correct expression for \( K_{\text {eq }} \), you need to remember that the equilibrium constant is based on the products and reactants of the reaction, raised to the power of their coefficients. In this case, the balanced equation is \( 2 \mathrm{SO}_{3}(g) = 2 \mathrm{SO}_{2}(g) + \mathrm{O}_{2}(g) \). Thus, \( K_{\text {eq }} \) will be formed from the concentrations of the products over the reactants, all raised to their respective coefficients. After analyzing the choices, B is the correct option as it reflects \( K_{\text {eq }}=\frac{\left[\mathrm{SO}_{2}\right]^{2}\left[\mathrm{O}_{2}\right]}{\left[\mathrm{SO}_{3}\right]^{2}} \). This ensures that the stoichiometry from the balanced reaction is accurately reflected in the equilibrium constant expression!