Chemistry Regents Practice Test

Which statement describes a system at equilibrium in the reaction N2O4(g) ⇌ 2NO2(g)?

1. The forward reaction occurs faster

2. The reverse reaction occurs faster

3. The rates of the forward and reverse reactions are equal

4. Only the forward reaction occurs

The correct answer is: The rates of the forward and reverse reactions are equal

In a chemical system at equilibrium, the rates of the forward and reverse reactions are equal, resulting in no net change in the concentrations of the reactants and products over time. In the case of the reaction N2O4(g) ⇌ 2NO2(g), this means that the rate at which N2O4 is converted to NO2 is equal to the rate at which NO2 is converting back to N2O4. At equilibrium, the concentrations of both N2O4 and NO2 remain constant, indicating that the system is balanced. This principle is central to the concept of dynamic equilibrium in reversible reactions, where both reactions continue to occur, but there is no observable change in the amounts of substances involved. In contrast, if either the forward or reverse reaction occurred faster than the other, it would indicate that the reaction is not at equilibrium, leading to a change in the concentrations of N2O4 or NO2. Therefore, only the option stating that the rates of the forward and reverse reactions are equal accurately describes a system at equilibrium.