Problem 108 - Chemistry: The Central Science

Question

Ozone in the upper atmosphere can be destroyed by the following two-step mechanism: $$ \begin{aligned} \mathrm{Cl}(g)+\mathrm{O}_{3}(g) & \longrightarrow \mathrm{ClO}(g)+\mathrm{O}_{2}(g) \\ \mathrm{ClO}(g)+\mathrm{O}(g) & \longrightarrow \mathrm{Cl}(g)+\mathrm{O}_{2}(g) \end{aligned} $$ (a) What is the overall equation for this process? (b) What is the catalyst in the reaction? (c) What is the intermediate in the reaction?

Step-by-Step Solution

Answer

(a) The overall equation for this process is: \(O_{3}(g) + O(g) \longrightarrow 2 O_{2}(g)\) (b) The catalyst in this reaction is Cl(g). (c) The intermediate in this reaction is ClO(g).

Step 1: Write down both reactions

Write down the two reactions in their respective steps: 1) Cl(g) + O3(g) → ClO(g) + O2(g) 2) ClO(g) + O(g) → Cl(g) + O2(g)

Step 2: Add the reactions and cancel common species

Add the two reactions and cancel out the common species on both sides of the reaction: 1) Cl(g) + O3(g) → ClO(g) + O2(g) 2) ClO(g) + O(g) → Cl(g) + O2(g) --------------------------------- Overall: O3(g) + O(g) → 2 O2(g) Hence, the overall equation for this process is: \(O_{3}(g) + O(g) \longrightarrow 2 O_{2}(g)\) (b) Catalysts speed up reactions but are not consumed in the process; they appear in the initial and final stages of the reaction but do not appear in the overall equation.

Step 3: Identify the catalyst

From the reactions above, we can see that Cl(g) is present in the reactants of the first step and in the products of the second step. Thus, Cl(g) is the catalyst in this reaction. (c) Intermediates are produced in one step of a reaction and then consumed in a later step; they do not appear in the overall equation.

Step 4: Identify the intermediate

From the reactions above, we can identify that ClO(g) is produced in the first step and then consumed in the second step. Therefore, ClO(g) is the intermediate in this reaction.