Which statement about Kc values is true?

Which statement about Kc values is true?

• A. Kc is independent of temperature.
• B. Kc depends only on initial concentrations.
• C. Kc depends on temperature.
• D. Kc remains constant regardless of reaction conditions.

Answer: (C)

The concept being tested is that the equilibrium constant Kc is tied to temperature through thermodynamics. Kc is determined by the standard free energy change of the reaction at a given temperature, since ΔG° = -RT ln K. Because ΔG°, and often ΔH°, can vary with temperature, the value of Kc changes when temperature changes. That’s why the equilibrium position shifts with temperature: for an exothermic reaction, increasing temperature tends to reduce Kc (move toward reactants); for an endothermic reaction, increasing temperature tends to increase Kc (move toward products). Initial concentrations don’t fix Kc; they only influence how the system reaches equilibrium under a particular temperature. So the correct statement is that Kc depends on temperature.

The concept being tested is that the equilibrium constant Kc is tied to temperature through thermodynamics. Kc is determined by the standard free energy change of the reaction at a given temperature, since ΔG° = -RT ln K. Because ΔG°, and often ΔH°, can vary with temperature, the value of Kc changes when temperature changes. That’s why the equilibrium position shifts with temperature: for an exothermic reaction, increasing temperature tends to reduce Kc (move toward reactants); for an endothermic reaction, increasing temperature tends to increase Kc (move toward products). Initial concentrations don’t fix Kc; they only influence how the system reaches equilibrium under a particular temperature. So the correct statement is that Kc depends on temperature.