JEE Chemistry 2025 Question with Solution

Given: The reaction is $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$.

Find: Which graph correctly shows attainment of equilibrium.

At equilibrium, the concentrations of reactants and products become constant, and the rates of the forward and reverse reactions become equal.

For this reaction, the concentrations of the reactants $H_2$ and $I_2$ decrease with time, while the concentration of the product $HI$ increases with time. As equilibrium is attained, all three concentrations become constant.

Therefore, the correct graph is the one in which $H_2$ and $I_2$ decrease and level off, while $HI$ increases and levels off.

The correct option is C.

Given: The reaction is $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$.

Find: The graph that correctly represents attainment of equilibrium.

1. Initially, the reactants $H_2$ and $I_2$ are consumed to form $HI$.
2. Therefore, the concentrations of $H_2$ and $I_2$ should decrease with time.
3. The concentration of $HI$ should increase with time.
4. When equilibrium is reached, the concentrations of all species stop changing and become constant.
5. Hence, the correct graph must show decreasing curves for $H_2$ and $I_2$ and an increasing curve for $HI$, all eventually becoming horizontal.

Final Answer: Option (3), so the correct option is C.