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

1. Unimolecular reaction
2. Trimolecular reaction
3. Bimolecular reaction

Step-by-step solution

Step-1: 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.

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

There is one reactant molecules involved in the reaction and hence it is called as a bimolecular reaction.

The rate expression for the reaction is given as $\text{rate=k}\left[BrN{O}_2\right]$.

Molecularity of the equation b:

The equation for the reaction

b) ${\text{OH+NO}}_2+{\text{Ar→HNO}}_3+Ar....\left(2\right)$

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

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

Step-3: Molecularity of the equation-c:

The equation for the reaction

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

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

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