The order of reaction: is defined as the total number of reactants whose concentrations
change during the course of a reaction. It the sum of exponents of the molar concentration
of the reactants in the rate equation of the reaction .
First order reaction
Second order reaction
THE CHARACTERSTIC OF ORDER OF REACTION:
1. The order of reaction cannot be obtained from a simple balanced equation, but it
can be known by experimental means.
2. The order depends on the conditions of the reaction.
3. The order may be a whole number ,fraction,or zero.
4. Theoretically, reaction of high order are possible but, it is doubtfull if reactions
higher than the third order exist.
The molecularity of a reaction: the molecularity of a reaction is defined as the
minimum number of atoms ,molecules,or ions of reactants taking part in the rate
determining step. The reactions are said to be unimolecular, biomolecular,or
trimolecular depending on whether one,two,or three molecules are involved during
the reaction.
Unimolecular reaction
BIOMOLECULAR REACTION
TRIOMOLECULAR REACTION
Characteristic of the molecularity:
1.molecularity refres to a one step reaction (rate determining step)of a complex
reaction involving a number of steps.
2.molecularity is always a whole number and is never a fraction or zero.
3.molecularity can be determined from a simple balanced equation and is thus a
theoretical concept.
4. molecularity reveals some fundamental facts about the reaction mechanism.
There is a difference between molecularity and order of reaction.