What defines chemical equilibrium in a reaction?

Chemical equilibrium in a reaction is defined by the condition where the rate of the forward reaction equals the rate of the reverse reaction. At this point, the concentrations of both reactants and products remain constant over time, even though both reactions are still occurring. This dynamic balance means that the system's macroscopic properties do not change, even though molecular-level processes are ongoing.

In a state of equilibrium, the system has not completed the conversion of all reactants into products; instead, there is a mixture of both. This is an essential concept in understanding how reversibility of reactions works.

Other choices suggest a different understanding of the nature of chemical reactions. For example, complete conversion implies that the reaction has gone to completion, which is not the case at equilibrium. The maximum concentration of reactants or the absence of reactants indicates that the reaction has moved beyond the equilibrium state or is not reversible, which does not properly describe equilibrium's dynamic nature.