Question

In what condition do order and molecularity of a reaction become equal?

Answer 1

Order of reaction:

• The order of the reaction is the connection that exists between the pace of a chemical reaction and the concentration of the species involved.
• The rate expression of the reaction in the issue must be known before the reaction order can be determined.

Molecularity of a reaction:

• A reaction's molecularity is defined as the number of reacting molecules that collide at the same time to produce a chemical reaction.
• In other terms, the number of reactant molecules involved in an elementary reaction is defined as its molecularity.

Condition for which order and molecularity of a reaction are equal:

• A reaction must be elementary in order for its order and molecularity to become equal.
• An elementary reaction is one that happens in a single step.
• The total of the whole reaction equation is the elementary reaction.
• Molecularity is derived at each stage in elementary processes.
• Consider the reaction shown below:

$\mathrm{A}+\mathrm{B}\to \mathrm{Products}$

$\mathrm{Rate}\mathrm{equation}={\left[\mathrm{A}\right]}^1{\left[\mathrm{B}\right]}^1$

• The order of the reaction is the sum of the coefficient of the rate equation.
• Therefore, the order of reaction $=2$
• And molecularity$=2$

Thus, for an equal value of order and molecularity, a reaction must be elementary.