What does the equilibrium constant represent in a chemical reaction?

The equilibrium constant is a crucial concept in chemical equilibrium that quantifies the relationship between the concentrations of reactants and products at equilibrium in a reversible reaction. When a reaction reaches equilibrium, the rates of the forward and reverse reactions become equal, and the concentrations of the reactants and products remain constant over time.

The equilibrium constant specifically represents the ratio of the concentrations of the products raised to their respective coefficients in the balanced chemical equation to the concentrations of the reactants raised to their respective coefficients. This ratio is established at equilibrium and is denoted as K_eq.

Thus, when a reaction is denoted as:

aA + bB ⇌ cC + dD,

the equilibrium constant (K_eq) can be expressed as:

K_eq = [C]^c [D]^d / [A]^a [B]^b

This formulation emphasizes that at equilibrium, the balance of concentrations reflects the relationship between products and reactants.

The other choices do not accurately capture the definition of the equilibrium constant: the first suggests a ratio without specifying it is at equilibrium, the third incorrectly suggests a total concentration rather than a ratio, and the fourth refers to the rate of change instead of the state of the system at equilibrium. Thus, the