Exercise 7 | Chemical Kinetics: Mechanisms

Here is a reaction: 2 NO (g) + Cl(g) → 2 NOCl (g).

The rate of this reaction is k [NO]2[Cl2].


Is the following mechanism plausible for this reaction?

NO (g) + Cl2 (g) NOCl (g) + Cl (g)   (fast, equilibrium)

NO (g) + Cl(g) → NOCl (g)   (slow)

Let’s determine the rate of the reaction if the mechanism is correct:

rate of the reaction = rate of the slow step = k[NO][Cl]


First step: fast equilibrium: k1 [NO][Cl2] = k-1 [NOCl][Cl]

⇒ [Cl] = k1 [NO][Cl2] / k-1 [NOCl] = K [NO][Cl2]/ [NOCl]


rate of the reaction = k[NO][Cl] = k’ [NO]2[Cl2]/[NOCl]

⇒ The mechanism is not plausible