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