Question:medium
Which of the following is a zero order reaction?
Which of the following is a zero order reaction?
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Surface catalyzed reactions often show zero-order kinetics when catalyst surface is fully occupied.
Updated On: May 14, 2026
- Decomposition of \( \text{H}_2\text{O}_2 \) catalysed by iodide in alkaline medium
- Artificial radioactive decay of unstable nuclei
- Decomposition of \( \text{N}_2\text{O}_5 \)
- Decomposition of \( \text{N}_2\text{O} \)
- Decomposition of gaseous ammonia on a hot platinum surface
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The Correct Option is
Solution and Explanation
Step 1: Understanding the Concept:
A zero-order reaction is a reaction whose rate is independent of the concentration of the reactants. The rate is constant over time. We need to identify which of the given examples fits this description.
Step 2: Detailed Explanation:
Let's analyze the order of each reaction listed:
(A) Decomposition of H\(_2\)O\(_2\) catalysed by iodide in alkaline medium: This reaction, 2H\(_2\)O\(_2\) \(\rightarrow\) 2H\(_2\)O + O\(_2\), catalyzed by I\(^-\), is an example of a first-order reaction. The rate is proportional to [H\(_2\)O\(_2\)].
(B) Artificial radioactive decay of unstable nuclei: All radioactive decay processes follow first-order kinetics. The rate of decay is proportional to the number of undecayed nuclei.
(C) Decomposition of N\(_2\)O\(_5\): The gas-phase decomposition of dinitrogen pentoxide, 2N\(_2\)O\(_5\)(g) \(\rightarrow\) 4NO\(_2\)(g) + O\(_2\)(g), is a classic example of a first-order reaction.
(D) Decomposition of N\(_2\)O: The decomposition of nitrous oxide is generally first-order at high pressures and second-order at low pressures. It is not typically zero-order.
(E) Decomposition of gaseous ammonia on a hot platinum surface: The reaction is 2NH\(_3\)(g) \(\xrightarrow{\text{Pt catalyst}}\) N\(_2\)(g) + 3H\(_2\)(g). At high pressure, the surface of the platinum catalyst becomes saturated with NH\(_3\) molecules. Once the surface is saturated, the rate of reaction no longer depends on the concentration (or pressure) of ammonia in the gas phase. The rate is limited by the number of available active sites on the catalyst, making it a zero-order reaction.
Step 3: Final Answer:
The decomposition of gaseous ammonia on a hot platinum surface is a textbook example of a zero-order reaction. This corresponds to option (E).
A zero-order reaction is a reaction whose rate is independent of the concentration of the reactants. The rate is constant over time. We need to identify which of the given examples fits this description.
Step 2: Detailed Explanation:
Let's analyze the order of each reaction listed:
(A) Decomposition of H\(_2\)O\(_2\) catalysed by iodide in alkaline medium: This reaction, 2H\(_2\)O\(_2\) \(\rightarrow\) 2H\(_2\)O + O\(_2\), catalyzed by I\(^-\), is an example of a first-order reaction. The rate is proportional to [H\(_2\)O\(_2\)].
(B) Artificial radioactive decay of unstable nuclei: All radioactive decay processes follow first-order kinetics. The rate of decay is proportional to the number of undecayed nuclei.
(C) Decomposition of N\(_2\)O\(_5\): The gas-phase decomposition of dinitrogen pentoxide, 2N\(_2\)O\(_5\)(g) \(\rightarrow\) 4NO\(_2\)(g) + O\(_2\)(g), is a classic example of a first-order reaction.
(D) Decomposition of N\(_2\)O: The decomposition of nitrous oxide is generally first-order at high pressures and second-order at low pressures. It is not typically zero-order.
(E) Decomposition of gaseous ammonia on a hot platinum surface: The reaction is 2NH\(_3\)(g) \(\xrightarrow{\text{Pt catalyst}}\) N\(_2\)(g) + 3H\(_2\)(g). At high pressure, the surface of the platinum catalyst becomes saturated with NH\(_3\) molecules. Once the surface is saturated, the rate of reaction no longer depends on the concentration (or pressure) of ammonia in the gas phase. The rate is limited by the number of available active sites on the catalyst, making it a zero-order reaction.
Step 3: Final Answer:
The decomposition of gaseous ammonia on a hot platinum surface is a textbook example of a zero-order reaction. This corresponds to option (E).
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