Question

For the given reaction, choose the correct expression of \(K_c\)​ from the following: \(Fe_{(aq)}^{3+}​+SCN_{(aq)}^{−}​⇌(FeSCN)_{(aq)}^{2+}\)​

• A. \( K_c = \frac{[\text{FeSCN}^{2+}]}{[\text{Fe}^{3+}][\text{SCN}^-]} \)
• B. \( K_c = \frac{[\text{Fe}^{3+}][\text{SCN}^-]}{[\text{FeSCN}^{2+}]} \)
• C. \( K_c = \frac{[\text{FeSCN}^{2+}]}{[\text{Fe}^{3+}]^2[\text{SCN}^-]^2} \)
• D. \( K_c = \frac{[\text{FeSCN}^{2+}]^2}{[\text{Fe}^{3+}][\text{SCN}^-]} \)

Answer 1

The Correct Option is A

The equilibrium constant, \(K_c\), is determined by dividing the product of the molar concentrations of the products, each raised to the power of its stoichiometric coefficient, by the product of the molar concentrations of the reactants, each raised to the power of its stoichiometric coefficient.

For the reaction:

\(\text{Fe}_{(aq)}^{3+} + \text{SCN}_{(aq)}^{-} \rightleftharpoons (\text{FeSCN})_{(aq)}^{2+}\),

the balanced equation indicates a 1:1:1 molar ratio. Therefore, the equilibrium constant \( K_c \) is expressed as:

\(K_c = \frac{[\text{FeSCN}^{2+}]}{[\text{Fe}^{3+}][\text{SCN}^-]}\).

Evaluating the provided options:

• \(K_c = \frac{[\text{FeSCN}^{2+}]}{[\text{Fe}^{3+}][\text{SCN}^-]}\): This expression aligns with the stoichiometric coefficients of the reaction. It is the correct representation.
• \(K_c = \frac{[\text{Fe}^{3+}][\text{SCN}^-]}{[\text{FeSCN}^{2+}]}\): This represents the reciprocal of the correct expression and is therefore incorrect.
• \(K_c = \frac{[\text{FeSCN}^{2+}]}{[\text{Fe}^{3+}]^2[\text{SCN}^-]^2}\): This option incorrectly applies exponents to the reactant concentrations, deviating from the stoichiometry.
• \(K_c = \frac{[\text{FeSCN}^{2+}]^2}{[\text{Fe}^{3+}][\text{SCN}^-]}\): This option incorrectly applies an exponent to the product concentration, which is not supported by the balanced equation.

Consequently, the accurate expression for the equilibrium constant \( K_c \) is:

\(K_c = \frac{[\text{FeSCN}^{2+}]}{[\text{Fe}^{3+}][\text{SCN}^-]}\).