What does the equilibrium constant (K) represent in a chemical reaction?

The equilibrium constant (K) is a fundamental concept in chemistry that quantifies the ratio of the concentrations of products to reactants at equilibrium for a given chemical reaction. When a reaction reaches dynamic equilibrium, the rates of the forward and reverse reactions are equal, leading to stable concentrations of reactants and products. The expression for K varies depending on the type of reaction but generally takes the form of a fraction: the concentration of products raised to the power of their coefficients over the concentration of reactants raised to the power of their coefficients.

This ratio reflects the tendency of the reaction to favor products or reactants under a specific set of conditions (temperature, pressure, etc.). Therefore, understanding K helps chemists predict how changes in conditions can shift the equilibrium position, aligning with Le Chatelier's principle. The other options do not accurately define what the equilibrium constant is; K specifically focuses on the concentrations involved in a reaction at equilibrium rather than pressures, reaction rates, or changes over time.