Molecularity of React ion Chemistry Notes
Molecularity of Reaction :
→ The total number of molecules of reactants taking part in elementary step of reaction is known as molecularity of reaction. Its value is always in whole number. So, the reaction is called unimolecular, bimolecular and trimolecular on participating one, two and three molecules respectively.
NH4 NO2 → N2 + 2H2O
The molecularity of this reaction is one.
H2 + I2 → 2HI
The molecularity of this reaction is two.
3KClO → KClO3 + 2KCl
The molecularity of this reaction is three.
→ Hence, molecularity of simple reactions is equal to the sum of number of various reactant molecules in balanced equations. Molecularity is never possible more than three. On the basis of molecularity, reactions can be divided in to following parts:
Simple Reactions. The reactions whose molecularity is equal to the number of their reactants, are called simple reactions.
O2F2 → O2 + F2
Molecularity = 1
2NO + OO2 → 2NOO2
Molecularity = 3
→ Complex Reactions : The reactions in which the number of reactants is more than three, generally take place in two or more steps. The slowest step in the reaction is called rate determining step. In such reactions, there is no importance of molecularity of reaction. The molecularity of such reaction is equal to total number of reactants, molecules or ions present in elementary step which is represented in the form of order of reaction.
4HBr + O2 → 2H2O + 2Br2
Rate = k [HBr) [O2]
We represent it by rate law.