Question
For the reaction $A \rightleftharpoons B$, variation of concentration is plotted against time as shown below.
Which of the following statements is true?
This question was previously asked in
WBJEE 2026 Physics and Chemistry Question Paper (24-May-2026)
The correct answer is
Region (3) indicates equilibrium
To determine which region indicates equilibrium in the reaction \(A \rightleftharpoons B\), we need to understand what equilibrium means in a chemical context. Chemical equilibrium occurs when the rate of the forward reaction equals the rate of the reverse reaction, so the concentrations of the reactants and products remain constant over time.
In the given concentration vs. time graph:
- In Region (1), the concentrations of A and B are changing significantly. This indicates the system has not yet reached equilibrium.
- In Region (2), although the rate of change is slowing, the concentrations are still adjusting. This suggests that equilibrium has not been achieved.
- Region (3) shows constant concentrations of A and B over time, indicating that the rates of the forward and backward reactions are equal. This is the state of equilibrium.
Since Region (3) represents the state where the concentrations of A and B are no longer changing, it indicates that the reaction has reached equilibrium.
Conclusion: The correct answer is Region (3) indicates equilibrium.
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