Question 14.6.2: Chlorofluorocarbons break down in the upper atmosphere to fo......
Chlorofluorocarbons break down in the upper atmosphere to form, among other products, chlorine atoms. The chlorine atoms are involved in the breakdown of ozone via the following mechanism.
Step 1. Cl(g) + O_{3}(g) → ClO(g) + O_{2}(g)
Step 2. ClO(g) + O_{3}(g) → Cl(g) + 2 O_{2}(g)
a. Identify the molecularity of each step in the mechanism.
b. Write the net reaction.
c. Identify any intermediates and/or catalysts in this mechanism.
You are asked to identify the molecularity of the steps in a mechanism, to write a net reaction, and to identify any catalysts or intermediates in the mechanism.
You are given a multistep mechanism.
a. Both steps in the mechanism involve two reactants, so both are bimolecular elementary steps.
b. The net reaction is found by adding the mechanism steps together and cancelling any species common to both reactants and products.
Step 1. Cl(g) + O_{3}(g) → ClO(g) + O_{2}(g)
Step 2. ClO(g) + O_{3}(g) → Cl(g) + 2 O_{2}(g)
\cancel{\text{Cl(g)}}+\cancel{\text{ClO(g)}}+2\text{ O}_{3}\text{(g)}\longrightarrow \cancel{\text{Cl(g)}}+\cancel{\text{ClO(g)}}+3\text{ O}_{2}\text{(g)}
Net reaction: 2 O_{3}(g) → 3 O_{2}(g)
c. Cl(g) is consumed in the first step and then produced in its original form in the second step; it is a catalyst in this mechanism. The species ClO is produced in the first step and then consumed in the second step; it is an intermediate in this mechanism. Note that neither the catalyst nor intermediate appear in the net reaction.