Question:
Which of the following is a first order reaction?
Which of the following is a first order reaction?
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Remember that enzyme-catalyzed reactions and gas decompositions on metal surfaces are usually zero-order under high-concentration conditions, whereas radioactive decay and simple hydrogenations are typically first-order.
Updated On: Apr 29, 2026
- Decomposition of ammonia on Pt surface at high temperature.
- Hydrogenation of ethene to ethane.
- Decomposition of HI on gold surface.
- Hydrolysis of ethyl acetate in the presence of NaOH.
- Oxidation of KI by peroxy disulphate.
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
The order of a reaction is an experimental quantity that describes the relationship between the rate of a chemical reaction and the concentration of its reactants.
Step 3: Detailed Explanation:
Let's analyze the kinetics of each given reaction:
- Option A & C: The decomposition of gases (like \(NH_3\) or \(HI\)) on a metal catalyst surface (Pt, Au) at high pressure/temperature follows zero-order kinetics because the catalyst surface becomes saturated.
- Option B: The hydrogenation of ethene (\(C_2H_4 + H_2 \to C_2H_6\)) is a classic example of a first-order reaction with respect to the hydrocarbon.
- Option D: Hydrolysis of an ester with a strong base (saponification) is a second-order reaction.
- Option E: The reaction between \(KI\) and peroxy disulphate is also a second-order reaction.
Step 4: Final Answer:
Hydrogenation of ethene is a first-order reaction.
The order of a reaction is an experimental quantity that describes the relationship between the rate of a chemical reaction and the concentration of its reactants.
Step 3: Detailed Explanation:
Let's analyze the kinetics of each given reaction:
- Option A & C: The decomposition of gases (like \(NH_3\) or \(HI\)) on a metal catalyst surface (Pt, Au) at high pressure/temperature follows zero-order kinetics because the catalyst surface becomes saturated.
- Option B: The hydrogenation of ethene (\(C_2H_4 + H_2 \to C_2H_6\)) is a classic example of a first-order reaction with respect to the hydrocarbon.
- Option D: Hydrolysis of an ester with a strong base (saponification) is a second-order reaction.
- Option E: The reaction between \(KI\) and peroxy disulphate is also a second-order reaction.
Step 4: Final Answer:
Hydrogenation of ethene is a first-order reaction.
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