Question

What happens to the half-life period for a first-order reaction, if the initial concentration of the reactants is increased?

• A. Increases
• B. Decreases
• C. Remains unchanged
• D. Increases and then decreases.

Answer 1

The correct option is C

Remains unchanged

Explanation for correct option:

C. Remains unchanged

Half life for a first-order reaction:

• “The half-life of a reaction is the time in which the concentration of a reactant is reduced to one half of its initial concentration”
• . It is represented as ${\mathrm{t}}_{1/2}$.
• For the first-order reaction, the half-life is expressed as:

${\mathrm{t}}_{1/2}=\frac{0.693}{\mathrm{k}}$, where $\mathrm{k}$ is the rate constant.

• The half-life period is constant, i.e., it is independent of the initial concentration of the reacting species.
• Thus, on increasing the initial concentration, the half-life remains unchanged.

Explanation for incorrect options:

As, on increasing the initial concentration, the half-life remains unchanged. Thus, options A, B, and D stand incorrect.

Hence, the correct choice is option C i.e. the half-life remains unchanged.