Chemical Kinetics

Rahul you are right....this doubt i had in mind few months back

order of a chemical reaction determined experimentally only...but i have come across several Qs which ask the order of rxn just by giving the balanced reaction.But actually from there u only get the molecularity of reaction only.However order is not always equal to the molecularity of rxn.

After asking a few taechers and discussing with users i got to know there are only certain rxns whose order u should know as a fact...these rxn are available in NCERT in Chem. Kinetics

order can only be determined by elementary reaction and not by looking at the balanced chemical equation.

Reactions can be either of the two- Elementary or Complex.

ELementary(SIngle Step Mech.) - The balanced Eqn. gives the order.

Complex(Multi Step Mech.) - The balanced slowest step rxn gives the order.

(Why we call it "EXperimentally determined" is because we can't just predict whether the rxn is elementary or, guess its mechanism by merely lookin if not...These are stated/worked out on the basis of experimental data only.)

thanks avik. my main doubt was that only

wikipedia=avik ........... long live :)

2A + 4B → C + D

so rate of reaction = \frac{-1d[A]}{2dt}= k [A]^{2}[B]^{4}

now multiply equation by 2

so 4A + 8B →2C + 2D

so rate of reaction =\frac{-1d[A]}{ldt}=k[A]^{m}[B]^{n}

so l , m , n = ???

pls giv reasons

Ans) l = n =4
m =2 ???

m and n will be same (i.e. 2 and 4 respectively) as they represent the orders of the reaction which is constant. (definitely correct)

even l =2 (doubt only here) (there is some confusion regarding this which was cleared by manish bhaiya)

see this
http://www.targetiit.com/iit-jee-forum/posts/kinetics-14705.html
and this

http://www.chemicalforums.com/index.php?topic=39807.msg152265#msg152265 (better discussion)