- Dynamic equilibrium is a state where the forward and reverse reaction rates are equal.
- The chemical reaction does not stop at equilibrium; it remains active (dynamic).
- Relative concentrations of products and reactants are not the defining factor for equilibrium.
- The final answer is \(\boxed{d}\).
Explanation
- Understanding Dynamic Equilibrium
Dynamic equilibrium is a fundamental concept in chemical kinetics and thermodynamics, describing a state in a reversible chemical reaction. In a reversible reaction, such as the one provided:
\[2 \text{SO}_2(g) + \text{O}_2(g) \longleftrightarrow 2 \text{SO}_3(g)\]
the reactants combine to form products, while at the same time, the products decompose to reform the reactants. Dynamic equilibrium occurs when the rate of the forward reaction (production of \(\text{SO}_3\)) exactly equals the rate of the reverse reaction (decomposition of \(\text{SO}_3\) back into \(\text{SO}_2\) and \(\text{O}_2\)).
- Evaluating the Options
We analyze the provided options:
A"When the concentration of the reactants is higher than the concentration of the products": This describes a specific state of the reaction mixture at equilibrium, but equilibrium is not defined by the relative quantities of substances. The concentrations remain constant at equilibrium, but they do not have to be equal to each other, nor do they follow a strict hierarchy.
B"When the forward and reverse reactions stop": The term "dynamic" explicitly means that the reactions continue to occur. At equilibrium, the system is not static; particles are constantly reacting in both directions.
C"When the rate of the forward reaction is higher than the rate of the reverse reaction": If the rates were unequal, there would be a net change in the amounts of reactants and products, meaning the system would not yet be at equilibrium.
D"When the rates of the forward and reverse reactions are equal": This is the definition of dynamic equilibrium. Once these rates match, the macroscopic properties of the system (like concentration, pressure, and color) no longer change over time.
- Conclusion
Based on our analysis, the correct condition for dynamic equilibrium is when the rate of the forward reaction equals the rate of the reverse reaction. Thus, option (d) is the correct description. The final answer is \(\boxed{d}\).
Examples
Consider a busy store with a constant number of customers inside. Even if people are constantly walking in through the front door and others are leaving through the back door, if the rate of people entering equals the rate of people leaving, the total number of people inside the store remains steady. This is a real-world parallel to dynamic equilibrium, where constant activity in both directions keeps the net state of the system unchanged. In chemistry, these "people entering and leaving" correspond to molecules transforming between reactants and products.