Target Exam

CUET

Subject

Chemistry

Chapter

Physical: Chemical Kinetics

Question:

Read the passage carefully and answer the Questions.

The decomposition of $N_2O_5 (g)$ is given as

$N_2Os (g) → 2NO_2(g) +\frac{1}{2}O_2(g)$

The above reaction is found to be of first order.

Select the correct statement for the half life of the given reaction

Options:

Half life is independent of the initial concentration of $N_2O_5$

Half life is directly proportional to the initial concentration of $N_2O_5$

Half life depends on the final concentration of all the species present in the reaction.

Half life is directly proportional to the rate constant.

Correct Answer:

Half life is independent of the initial concentration of $N_2O_5$

Explanation:

The correct answer is Option (1) → Half life is independent of the initial concentration of $N_2O_5$

For a first-order reaction, the half-life is given by:

$t_{1/2} = \frac{0.693}{k}$​

From this expression:

  • It does not contain the initial concentration of the reactant.
  • It is inversely proportional to the rate constant $k$.

 Half life is independent of the initial concentration of N₂O₅Correct

 Half life is directly proportional to the initial concentration → Incorrect
 Half life depends on the final concentration of all species → Incorrect
 Half life is directly proportional to the rate constant → Incorrect (it is inversely proportional)