What characterizes chemical equilibrium?

Chemical equilibrium is characterized by a dynamic state in which the rates of the forward and reverse reactions are equal, meaning that the concentrations of reactants and products remain constant over time. This balance does not imply that the substances involved are in equal amounts; rather, it indicates that there is a consistent and ongoing conversion between reactants and products occurring at a constant rate.

At equilibrium, although the reaction appears to have 'stopped' because there are no changes in the concentrations of reactants and products, the chemical processes are still actively happening in both directions. This is fundamental in understanding how reversible reactions operate and is crucial in fields like chemical engineering, biochemistry, and environmental science.

The other choices do not correctly define equilibrium. Complete consumption of reactants suggests that the reaction has gone to completion without a reversal, which is contrary to the concept of equilibrium. Unequal rates of the forward and reverse reactions imply that the system is still moving toward equilibrium but has not yet reached that state. Finally, the idea that products begin to exceed reactants describes a process in motion rather than a stable equilibrium.