Order Of Reaction
For a first-order reaction, the half-life is 20 minutes. The time required for 75% completion is:
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About This Question
- Subject
- chemistry
- Chapter
- chemical kinetics
- Topic
- order of reaction
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
40 minutes
For a First-Order Reaction, the half-life (t1/2) is constant.
- Let [A]0 be the initial concentration.
- After 1st half-life (20 min), [A]=50% of [A]0.
- After 2nd half-life (another 20 min), [A]=50% of 50%=25% of [A]0.
- 75% completion means 25% reactant is remaining.
- Total time =1st half-life +2nd half-life =20+20=40 minutes. Alternatively, for first order, t75%=2×t50%.
This easy difficulty chemistry question is from the chapter chemical kinetics, covering the topic of order of reaction. It appeared in the 2025 exam.
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