Exercise 8 | Chemical Kinetics: Mechanisms

Here is a reaction: Cl2(g) + CO(g) → Cl2CO(g).

The rate of this reaction is k[CO][Cl2]3/2.

Is the following mechanism plausible for this reaction?

(1) Cl2 2 Cl (fast, equilibrium)

(2) Cl + Cl2 Cl3 (fast, equilibrium)

(3) Cl3 + CO → Cl2CO + Cl (slow)

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

rate of the reaction = rate of the slow step = k[CO][Cl3]


First step: fast equilibrium: k1 [Cl2] = k-1 [Cl]2

Second step: fast equilibrium: k2 [Cl][Cl2] = k-2 [Cl3]

⇒ [Cl3] = K2 [Cl][Cl2] and [Cl] = K1[Cl2]1/2

⇒ [Cl3] = K [Cl2]3/2


rate of the reaction = k[CO][Cl3] = k’[CO] [Cl2]3/2

⇒ The mechanism is plausible