What equation relates the concentration of products and reactants at equilibrium?

The correct response is based on the concept of the equilibrium constant expression, which is fundamental in chemical equilibrium. The equilibrium constant expression provides a mathematical relationship that quantitatively describes the ratio of the concentrations of the products to the concentrations of the reactants at equilibrium, each raised to the power of their respective coefficients from the balanced chemical equation.

At equilibrium, the rates of the forward and reverse reactions are equal, and the concentrations of all species remain constant. The equilibrium constant (K) is defined for a particular reaction at a given temperature and is crucial for predicting the direction in which a reaction will proceed when not at equilibrium.

For a general reaction:

aA + bB ⇌ cC + dD

the equilibrium constant expression is written as:

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

This expression illustrates how changes in concentration can affect the position of equilibrium and allows chemists to predict the extent of the reaction under various conditions, which is vital for many applications in chemical engineering, synthesis, and understanding reaction dynamics.