At high pressure the following reaction is zero order.
$2 N H_{3} (g) 1130 K - ---------- \to P l a t i n i u m c a t a l y s t N_{2} (g) + 3 H_{2} (g)$ Which of the following options are correct for this reaction?
(a)Rate of reaction = Rate constant
(b)Rate of the reaction depends on concentration of ammonia
(c)Rate of decomposition of ammonia will remain constant until ammonia disappears completely
(d)Further increase in pressure will change the rate of reaction

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Solution

Answers: (a), (c), and (d).

Given, chemical reaction is
$2 N H_{3} (g) 1130 K - ---------- \to P l a t i n i u m c a t a l y s t N_{2} (g) + 3 H_{2} (g)$
At very high pressure reaction become independent of concentration of ammonia i.e., zero order reaction
Hence, $R a t e = k [ρ_{N H_{3}}]^{0}$
Rate =k
(a) The rate of reaction = Rate constant
(c) Rate of decomposition of ammonia will remain constant until ammonia disappears completely. •
(d) Since, formation of ammonia is a reversible process further increase in pressure will change the rate of reaction. According to Le-Chatelier principle increase in pressure will favour in backward reaction.

Note: For a zero order reaction, the rate of reaction is independent of the concentration of ammonia. Hence, the statement (b) is wrong.

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