What is the molecularity of reaction?
The total number of reactant molecules or atoms taking part in the chemical reaction is known molecularity of the reaction.
Three types of molecularity of reaction are; Unimolecular reaction, Bimolecular reaction, and Trimolecular reaction.
Unimolecular reaction
The unimolecular reaction occurs during a chemical reaction; only one molecule is involved in a chemical reaction.
Bimolecular reaction
A bimolecular reaction occurs during a chemical reaction when two molecules participate in a chemical reaction.
Trimolecular reaction
A trimolecular reaction occurs during a chemical reaction when three molecules take part in a chemical reaction.
ORDER AND MOLECULARITY OF SIMPLE REACTION
There are several simple reactions studied in chemical kinetics, and we conclude that reaction order is the same as their molecularity. For example Decomposition of Nitrogen peroxide.
The above reaction order is one, and the molecularity of the reaction is also one. And is the same for the dissociation of hydrogen iodide; both are two, and that of the reaction involving a combination of nitric oxide and oxygen is 3.
But, this is not always the case. Many reactions have the order of reaction different from the molecularity of the reaction. This case is mainly when one reactant is present in significant excess. Examples are Hydrolysis of ethyl acetate and inversion of cane sugar in an aqueous solution.
Above reaction, the molecularity of each reaction is two, and the order of a reaction is one. The experiment rate of reaction is different in the concentration of ethyl acetate in the first case and that of sucrose in the second case.
Water is present in large amounts that in concentration (i.e. the number of moles/litre) remains constant in each case’s reaction course.
The reaction rate is different only with the concentration of the ester in the first case and that of sucrose in the second case; this reaction is known as Pseudo monomolecular reaction.
