Pseudo-first Order Reactions
The acid-catalysed hydrolysis of ethyl acetate in aqueous solution is an example of:
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About This Question
- Subject
- chemistry
- Chapter
- chemical kinetics
- Topic
- pseudo-first order reactions
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
Pseudo-first order reaction
The hydrolysis of ethyl acetate is: CH₃COOC₂H₅ + H₂O → CH₃COOH + C₂H₅OH. True rate = k[CH₃COOC₂H₅][H₂O], making it second order overall. However, since water is the solvent and is present in large excess (its concentration ≈ 55.5 mol L⁻¹ and remains virtually constant during the reaction), the term k[H₂O] is absorbed into a new pseudo rate constant k' = k[H₂O]. The observed rate law becomes rate = k'[CH₃COOC₂H₅], which follows first-order kinetics. Such reactions are called pseudo-first order reactions.
This medium difficulty chemistry question is from the chapter chemical kinetics, covering the topic of pseudo-first order reactions. It appeared in the 2025 exam.
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