Fe3+(aq) + SCN-(aq) ⇄ Fe(SCN)2+(aq) For the reaction represented above, the value of the equilibrium — Equilibrium Chemistry Question

STEPS:

1. Understand the Meaning of the Equilibrium Constant ($K_{eq}$): The equilibrium constant expression for the given reaction is $K_{eq} = \frac{[Fe(SCN)^{2+}]}{[Fe^{3+}][SCN^-]}$. This value represents the ratio of product concentrations to reactant concentrations when the system reaches equilibrium at a specific temperature.
2. Evaluate Statement II (Product vs. Reactant Favorability): A value of $K_{eq} > 1$ indicates that, at equilibrium, the concentration of the products (the numerator) is greater than the concentrations of the reactants (the denominator). Since the given $K_{eq}$ is 240, which is significantly greater than 1, the products are favored over the reactants at equilibrium. Thus, deduction II is correct.
3. Evaluate Statement I (Thermodynamics vs. Kinetics): The value of an equilibrium constant relates to the extent of a reaction (thermodynamics), not the speed at which it occurs (kinetics). A large $K_{eq}$ does not mean a reaction is "quite rapid"; it simply means that once equilibrium is eventually reached, there will be more products than reactants. Without information about the rate constant ($k$) or activation energy, we cannot deduce the speed of the reaction. Thus, deduction I is not necessarily correct.
4. Evaluate Statement III (Enthalpy): To determine if a reaction is endothermic ($\Delta H > 0$) or exothermic ($\Delta H < 0$), one must observe how the equilibrium constant changes with temperature. Because the problem only provides the value of $K_{eq}$ at a single temperature (25°C), there is no way to determine the sign of $\Delta H$. Thus, deduction III cannot be made.
5. Conclusion: Since only statement II is a valid deduction from the provided information, the correct choice is B.

WHY_OTHERS_WRONG:

• A) I only: This incorrectly assumes that a high equilibrium constant implies a fast reaction rate. $K_{eq}$ and reaction speed are independent concepts.
• C) I and II only: While II is correct, I is an invalid deduction because $K_{eq}$ provides no information about the kinetic "rapidity" of the process.
• D) II and III only: While II is correct, III is invalid because determining whether a reaction is endothermic requires $K_{eq}$ values at multiple temperatures to see the direction of the shift.
• E) I, II, and III: This choice incorrectly accepts all three statements, failing to distinguish between the thermodynamic extent of a reaction ($K_{eq}$), its kinetic rate (Statement I), and its temperature dependence (Statement III).