What does the equilibrium constant (Kc) indicate?

The equilibrium constant (Kc) is a valuable tool in understanding the behavior of a chemical reaction at equilibrium. Specifically, it indicates the position of the equilibrium of a reaction, quantifying the ratio of the concentrations of products to the concentrations of reactants when the reaction has reached a state of balance.

When Kc is calculated, it reflects how far the reaction proceeds before reaching equilibrium—providing insight into whether the equilibrium favors the reactants or products. A large Kc value suggests that at equilibrium, the concentration of products is significantly greater than that of reactants, indicating a product-favored reaction. Conversely, a small Kc value indicates reactants are favored, with a higher concentration of them compared to the products.

In contrast, the other options do not correctly represent the function of the equilibrium constant. The speed of the reaction relates to kinetics, not the equilibrium position. The amount of reactants present varies throughout the reaction and does not remain constant until equilibrium is achieved. Temperature affects the value of Kc but is not indicated by it directly.