Question Detail
Question
A certain first-order reaction A → B is 25% complete in 42 min at 25 °C. What is its rate constant?
Correct Answer
Option A is the correct answer.
Detailed Explanation
For first order: k = (1/t) ln([A]₀/[A]). If 25% complete, [A] = 0.75[A]₀. k = (1/42) ln(1/0.75) = (1/42) × 0.2877 = 0.00685 min⁻¹ ≈ 6.8 × 10⁻³ min⁻¹.
Hint
Use the integrated rate law for first-order reactions.