Question
Decomposition of $NH _{3( g )}$ on platinum surface at high temperature is a zero order reaction. Explain.
✓
Answer
The decomposition of $NH _{3( g )}$ on platinum surface is represented as,
$2 NH _{3( g )} \frac{1130 K }{ Pt } N _{2( g )}+3 H _{2( g )}$
Since it is a heterogeneous catalysed reaction, $NH_3$ gaseous molecules at high pressure are adsorbed on the metal surface covering the surface area.
The number of $NH _3$ molecules adsorbed is small compared to $NH _3$ molecules in the gaseous phase.
Only the molecules adsorbed on the surface get decomposed. Hence rate of the decomposition becomes independent of the concentration (pressure) of $NH _3$. Therefore the decomposition reaction is zero order.
$2 NH _{3( g )} \frac{1130 K }{ Pt } N _{2( g )}+3 H _{2( g )}$
Since it is a heterogeneous catalysed reaction, $NH_3$ gaseous molecules at high pressure are adsorbed on the metal surface covering the surface area.
The number of $NH _3$ molecules adsorbed is small compared to $NH _3$ molecules in the gaseous phase.
Only the molecules adsorbed on the surface get decomposed. Hence rate of the decomposition becomes independent of the concentration (pressure) of $NH _3$. Therefore the decomposition reaction is zero order.
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