Question

Identify each of the following elementary reactions as unimolecular, bimolecular, or termolecular, and write the rate expression.

(a) BrONO₂ → BrO + NO₂

(b) HO + NO₂ +Ar→ HNO₃+ Ar

(c) O + H₂S → OH + HS

Short answer

a)Unimolecular reaction

b) Trimolecular reaction

c) Bimolecular reaction

Step-by-step solution

Molecularity of the   equation a:

The number of reactant molecules involved in the elementary step of the reaction is defined as the molecularity of the reaction.

${\text{a)BrONO}}_2{\text{→BrO+NO}}_{\text{2}}\text{.........}\left(1\right)$

There is one reactent molecule involved in the reaction so called unimolecular reaction

The rate expression for the reaction is given as $\text{rate}=\text{k}\left({\text{BrONO}}_2\right)$

Molecularity of equation b:

The equation for the reaction

b) ${\text{OH+NO}}_2+\text{Ar}\to {\text{HNO}}_3+\hspace{0.17em}\text{Ar........}\left(2\right)$

There are three reactent molecules involved in the reaction and so the molecularity of the reaction is three.

The rate expression for the reaction is given as $\text{rate}=\left[\text{OH}\right]\left[{\text{NO}}_2\right]\left[\text{Ar}\right]$

Molecularity of equation c:

The equation for the reaction

C) $O+{\text{H}}_{2}S\to \text{OH+HS.......}\left(3\right)$

There is one reactent molecule involved in the reaction,so called unimolecular reaction.

The rate expression for the reaction is given as$\text{rate=k}\left[O\right]\left[{\text{H}}_{2}S\right]$