How is the equilibrium constant (K) calculated for a chemical reaction?

The equilibrium constant (K) for a chemical reaction quantifies the ratio of the concentration of products to the concentration of reactants at equilibrium, each raised to the power of their respective stoichiometric coefficients from the balanced chemical equation. This relationship reflects the balance achieved when the forward and reverse reactions occur at the same rate.

In the correct formulation, K is determined by taking the concentrations of the products, which are the substances formed in the reaction, and dividing that by the concentrations of the reactants, which are the starting substances. Each concentration is elevated to the power corresponding to the coefficient from the balanced equation. This approach emphasizes that K is a ratio that signifies the relative amounts of products versus reactants when the system is at equilibrium.

Understanding this principle is crucial because it allows chemists to predict how changes in conditions can affect the position of equilibrium, thereby influencing the yield of products in a reaction. The other options do not accurately reflect the method for calculating the equilibrium constant and introduce incorrect relationships or units.