When is equilibrium achieved in a reversible reaction contained in a closed system?

Equilibrium in a reversible reaction within a closed system is reached when the rates of the forward and reverse reactions are exactly the same. At this point, the concentration of reactants and products remains constant, even though both reactions continue to take place. This dynamic situation means that there is no net change in the concentration of the substances present in the system.

Understanding this concept is critical in the study of chemical reactions because it highlights the balance established during reversible processes. Neither reactants nor products achieve zero concentration; instead, they exist at specific levels that do not fluctuate once equilibrium is established.

The other scenarios described would indicate that equilibrium has not been reached. For instance, if the forward reaction is faster than the reverse reaction, the concentration of reactants would decrease while that of products would increase. Similarly, differing rates denote a lack of balance, and complete conversion of reactants to products would mean that the reverse reaction can no longer occur, which also signifies a lack of equilibrium.