Zero Order Reactions
For a zero-order reaction, the initial concentration of the reactant is 0.8 mol L⁻¹ and the rate constant k = 2 × 10⁻³ mol L⁻¹ s⁻¹. The half-life of the reaction is:
Select the correct option:
Solution
200 s
For a zero-order reaction, the integrated rate law is [A] = [A]₀ − kt. At half-life (t₁/₂), [A] = [A]₀/2. Substituting: [A]₀/2 = [A]₀ − k·t₁/₂, which gives t₁/₂ = [A]₀/(2k). Therefore, t₁/₂ = 0.8 / (2 × 2 × 10⁻³) = 0.8 / 0.004 = 200 s. Note that unlike first-order reactions, the half-life of a zero-order reaction depends on the initial concentration.
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About This Question
- Subject
- chemistry
- Chapter
- chemical kinetics
- Topic
- zero order reactions
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
200 s
For a zero-order reaction, the integrated rate law is [A] = [A]₀ − kt. At half-life (t₁/₂), [A] = [A]₀/2. Substituting: [A]₀/2 = [A]₀ − k·t₁/₂, which gives t₁/₂ = [A]₀/(2k). Therefore, t₁/₂ = 0.8 / (2 × 2 × 10⁻³) = 0.8 / 0.004 = 200 s. Note that unlike first-order reactions, the half-life of a zero-order reaction depends on the initial concentration.
This medium difficulty chemistry question is from the chapter chemical kinetics, covering the topic of zero order reactions. It appeared in the 2025 exam.
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