How is the equilibrium constant (K) defined in a chemical reaction?

The equilibrium constant, denoted as K, is defined as the ratio of the concentrations of products to the concentrations of reactants at equilibrium, raised to the power of their respective coefficients from the balanced chemical equation. This means that K quantifies the extent to which a reaction favors the formation of products at equilibrium compared to reactants.

In a general reaction, aA + bB ⇌ cC + dD, the equilibrium constant K can be formulated as:

[ K = \frac{[C]^c \times [D]^d}{[A]^a \times [B]^b} ]

This definition is crucial because it highlights that K is specific to a given reaction at a specific temperature, reflecting the dynamic balance between reactants and products. At equilibrium, the rates of the forward and reverse reactions are equal, which is why the concentrations remain constant, forming the basis of the equilibrium expression.

This definition also distinguishes it from other options. For instance, K being defined as the sum of products' concentrations does not capture the necessary relationship with reactants or their coefficients. Similarly, the notion of the ratio of products to reactants at any time does not only apply at equilibrium; it may give an inaccurate representation unless the system has