Question

What is the molecularity of a reaction? Is it different from the order of a reaction? Name one bimolecular and one trimolecular gaseous reaction.

Answer 1

Hint: Try to figure out what molecularity of a reaction means and how it is different from the order of the reaction. Remember that molecularity is always an integer greater than zero. Based on the value of integers we can classify a given reaction into different types.

Complete step by step answer:

We know that molecularity of a reaction is the number of molecules involved in the reaction to form desired products. This molecularity is the sum of stoichiometric coefficients of each reactant of a reaction. As stoichiometric coefficients are always integers, molecularity is also an integer and is always greater than zero. Molecularity does not depend on the intermediate steps of a reaction.
The order of a reaction is the sum of powers of reactants in the rate law of the reaction. > Where this rate law is derived experimentally. The order may or may not be an integer. It may be a positive or negative number. It may also be equal to zero. So it is different from the molecularity of the reaction.
- Bimolecular reactions involve 2 molecules of reactants in the formation of products.
$H_2 + Cl_2 → 2HCl$
- Trimolecular reactions involve 3 molecules of reactants in the formation of products.
$2NO + O_2 → 2NO_2$

Note: For some elementary reactions order of reaction will be equal to the molecularity of reaction but generally, the order of reaction can only be determined experimentally. Rate law gives ideas about the reactants which are actively involved in reaction.