What characteristic defines dynamic equilibrium in a chemical reaction?

Dynamic equilibrium in a chemical reaction is characterized by a state where the concentrations of reactants and products remain constant over time. This does not mean that the reactions have stopped; rather, it indicates that the rate at which the forward reaction occurs (where reactants are converted to products) is equal to the rate at which the reverse reaction occurs (where products are converted back into reactants). As a result, there is no net change in the concentrations of each species involved in the reaction.

In contrast, if the rate of the forward reaction were greater than that of the reverse reaction, the system would not be at equilibrium, and the concentrations of reactants and products would change over time. Additionally, dynamic equilibrium can occur in both closed and open systems, although it is most commonly described in the context of closed systems where the concentrations can stabilize. Lastly, in a dynamic equilibrium, reactants are not completely used up; instead, they coexist with products at stable concentrations.

Therefore, the statement that the concentrations of reactants and products remain constant accurately reflects the condition of dynamic equilibrium in a chemical reaction.