What does the equilibrium constant (K) quantify?

The equilibrium constant (K) quantifies the ratio of the concentrations of products to the concentrations of reactants in a chemical reaction that has reached equilibrium. This means that at equilibrium, the system has a specific ratio of products to reactants that remains constant at a given temperature.

In a reversible reaction, K is determined by the expression that relates the molar concentrations (or partial pressures) of the products raised to the power of their coefficients in the balanced chemical equation to the concentrations of the reactants raised to the power of their coefficients. This relationship provides insight into the position of equilibrium: a larger value of K indicates that the formation of products is favored, while a smaller value suggests reactants are favored.

The other options refer to unrelated concepts; for instance, the temperature of the reaction affects the value of K but is not what K itself measures. The speed of the reaction is described by reaction rates and does not pertain to equilibrium constants. Similarly, the energy released during the reaction relates to thermodynamic principles, such as enthalpy changes, rather than the equilibrium constant itself.