The decomposition of gaseous Ammonia on a hot platinum surface is a _______________ order reaction at high pressure.
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. zero.
The decomposition of gaseous ammonia (NH₃) on a hot platinum surface is a zero-order reaction at high pressure. This means the reaction rate remains constant and is independent of ammonia concentration, as the platinum surface becomes saturated with NH₃ molecules. At lower pressures, it may follow first-order kinetics, but under high pressure, the rate is solely determined by the catalyst's active sites.
Key point: Zero-order reactions occur when the rate is unaffected by reactant concentration.
Other options:
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First-order (one): Reaction rate depends on NH₃ concentration, observed at low pressure.
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Second-order (two): Rate depends on two reactant concentrations (unlikely here, as NH₃ decomposes alone).
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Third-order (three): Rare, requiring three reactant molecules (irrelevant to this reaction).
Thus, at high pressure, zero-order kinetics dominate due to catalyst saturation.