Chemistry - Chemical Kinetics Question with Solution | TestHub

An elementary reaction is one that occurs in a single step and has a single transition state.

The decomposition of ozone, ${\text{O}}_{3(g)}\to {\text{O}}_{2(g)}+{\text{O}}_{(g)}$, is a unimolecular elementary reaction.

The other reactions are complex and occur in multiple steps:

$2{\text{NO}}_2{\text{Cl}}_{(g)}\to 2{\text{NO}}_{2(g)}+{\text{Cl}}_{2(g)}$ occurs via:
Step 1: ${\text{NO}}_2\text{Cl}\to {\text{NO}}_2+\text{Cl}$ (slow)
Step 2: ${\text{NO}}_2\text{Cl}+\text{Cl}\to {\text{NO}}_2+{\text{Cl}}_2$ (fast)

$2{\text{NO}}_{2(g)}+{\text{F}}_{2(g)}\to 2{\text{NO}}_2{\text{F}}_{(g)}$ occurs via:
Step 1: ${\text{NO}}_2+{\text{F}}_2\to {\text{NO}}_2\text{F}+\text{F}$ (slow)
Step 2: ${\text{NO}}_2+\text{F}\to {\text{NO}}_2\text{F}$ (fast)

$2{\text{NO}}_{(g)}+{\text{Cl}}_{2(g)}\to 2{\text{NOCl}}_{(g)}$ occurs via:
Step 1: $\text{NO}+{\text{Cl}}_2\rightleftharpoons {\text{NOCl}}_2$ (fast)
Step 2: ${\text{NOCl}}_2+\text{NO}\to 2\text{NOCl}$ (slow)

Therefore, only the first reaction is elementary.

Answer: ${\text{O}}_{3(g)}\to {\text{O}}_{2(g)}+{\text{O}}_{(g)}$