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🧪 Chemistry  ·  Chemical Kinetics  ·  NEET & JEE

A first-order reaction has k = 0.231 min⁻¹. The time for 90% completion is:

Answer: 10 min.

  • A 10 min
  • B 3 min
  • C 15 min
  • D 6.93 min

Correct answer: A. 10 min

Explanation: t = (2.303/k) × log([A]₀/[A]) = (2.303/0.231) × log(100/10) = 9.97 × 1 ≈ 10 min.

First-Order Decay: Constant Half-Lifetime[A][A]₀[A]₀/22 × t½[A]₀/4Each successive half-life takes the SAME amount of time, regardless of starting concentration

First-order decay curve: concentration halves every t½, and that half-life is constant - a defining test for first-order kinetics.

Concept context

Study the speed of reactions and what affects it: concentration, temperature, and catalysts. Covers rate law, order of reaction, the Arrhenius equation, and reaction mechanisms step by step.

Read the full Chemical Kinetics notes →