Question

The half life of a first order reaction

• A. does not depend upon rate constant
• B. does not depend upon initial concentration
• C. depends upon initial concentration
• D. all of these

Hint:

For first-order reactions, half-life is constant and independent of initial concentration.

Answer 1

The Correct Option is B

Step 1: Formula of half-life.
For a first-order reaction, the half-life is given by: \[ t_{1/2} = \frac{0.693}{k} \] Step 2: Dependence.
From the formula, we see that the half-life depends only on the rate constant \(k\), not on the initial concentration of the reactant.
Step 3: Analyze options.
(A) Incorrect, it actually depends on \(k\).
(B) Correct, it does not depend on initial concentration.
(C) Wrong, half-life is independent of initial concentration.
(D) Wrong, since only (B) is correct.
Step 4: Conclusion.
Hence, the correct answer is (B) does not depend upon initial concentration.