What does the equilibrium constant (Kc) represent?

The equilibrium constant, denoted as Kc, represents the relationship between the concentrations of the products and reactants in a reversible chemical reaction at equilibrium. Specifically, when a reaction reaches equilibrium, the ratio of the concentration of products to the concentration of reactants, each raised to the power of their respective coefficients in the balanced equation, becomes constant. This means that Kc is a measure of the extent to which a reaction favors the formation of products at equilibrium.

In this context, the reaction quotient indicates the ratio of products to reactants at any point in time, and when the system reaches equilibrium, this quotient becomes equal to Kc. Therefore, option B accurately describes Kc as representing the reaction quotient at equilibrium. Understanding Kc is crucial for predicting the direction of the reaction, as well as for calculating the concentrations of reactants and products at equilibrium based on their initial concentrations.