Order : sum of the exponents of the molar concentration
in the rate law experesion.
Molecularity : The no. of atoms, ions, molecules, that must
collide with one another simultaneously to
results into a chemical reaction.
Order : This can be determine experimentally only.
Molecularity : This can be calculated by adding the no. of
molecules in the lower step.
Order : This can't be determined by looking at the
stochiometry of coefficient.
Molecularity :This can be determine by looking at the at
the stochiometry cofficent.
Order : It need not to be a whole no. it can be fraction, or
zero.
Molecularity : It is always a whole no.


aA+bB to give product P
Then rate expression for this reaction is
Rate is directly proportional to [ A ] to the power m * [B] to
the power n.
Then order of the reaction with respect to reactant A is m
and the order of the reaction w.r.t B is n.
And the molecularity of the reaction is a+b.