Question

For the first order reaction A → B, the rate constant is 0.25 s\(^{-1}\), if the concentration of A is reduced to half, the value of the rate constant will be

• A. 2.25 s\(^{-1}\)
• B. 0.075 s\(^{-1}\)
• C. 0.30 s\(^{-1}\)
• D. 0.25 s\(^{-1}\)

Hint:

In first-order reactions, the rate constant is independent of the concentration of reactants.

Answer 1

The Correct Option is D

Step 1: Understanding first-order reactions.
For a first-order reaction, the rate constant \( k \) remains constant regardless of the concentration of reactants. Hence, when the concentration of A is halved, the rate constant will not change.

Step 2: Analyzing the options.
(A) 2.25 s\(^{-1}\): Incorrect — The rate constant does not change for first-order reactions.
(B) 0.075 s\(^{-1}\): Incorrect — The rate constant remains the same.
(C) 0.30 s\(^{-1}\): Incorrect — The rate constant is unchanged.
(D) 0.25 s\(^{-1}\): Correct — The rate constant for a first-order reaction remains constant.

Step 3: Conclusion.
The correct answer is (D) 0.25 s\(^{-1}\), as the rate constant for a first-order reaction does not change with concentration.