ACS Chemistry Practice Exam 2026 – The All-in-One Guide to Exam Success!

In a chemical equilibrium, the concentrations of reactants and products reach a state where they no longer change over time, although the chemical reactions continue to occur in both the forward and reverse directions. This dynamic balance means that the rate of formation of products equals the rate of consumption of reactants. As a result, while individual molecules are still reacting, the overall concentrations of reactants and products remain constant.

Understanding this concept is crucial because it highlights the nature of reversible reactions and the concept of dynamic equilibrium. When a system is at equilibrium, even though the reactions are ongoing, there is no net change in the amounts of the reactants and products. Hence, the correct answer reflects this principle of equilibrium, indicating that both reactants and products are maintained at constant concentrations despite continuous reaction activity.