Chemical Kinetics Part - 2

Factors Affecting Rate of Reaction:

ü Concentration of reactant

ü Surface area

ü Temperature

ü Nature of reactant

ü Presence of catalyst.

Dependence rate on Concentration:

Rate Law: The rate of reaction is directly proportional to the product of concentration of reactant and each concentration is raised to some power which may or may not be equal to stereochemistry experimentally.

For a general reaction, aA + bB → cC + dD,

Rate α [A]^x[B]^y

Rate = k[A]^x[B]^y (Where x and y may or may not equal to a & b).

k is proportionality constant and is called Rate Constant.

Rate Constant (k): Rate constant is a rate of reaction when molar concentration of reactant is unity.

Molecularity of a Reaction: The no. of molecules of the reactants involved in the reaction is known as Molecularity. It cannot be zero or fractional. It can have values 1,2,3 etc. it is applicable only to elementary reactions.

If the molecularity of a reaction is 1, it is called Unimolecular Reaction. e.g. Decomposition of ammonium nitrite NH₄NO₂ → N₂ + 2 H₂O.

If the molecularity of a reaction is 2, it is called Bimolecular Reaction. e.g. Decomposition of Hydrogen Iodide 2 HI → H₂ + I₂

Order of Reaction: Order is the sum of the powers of the concentration terms of the reactants in the rate law. It is an experimental quantity. It can have the values 0,1,2,3… or a fraction. It is applicable to both elementary and complex reactions.

For a general reaction, aA + bB → cC + dD

r = k[A]x[B]y, Order of the reaction = x + y

If the order of a reaction is zero, it is called Zero Order Reaction, if it is one, it is called First Order Reaction, if it is two, it is called Second Order Reaction and so on.

S.No.	Order	Molecularity
1.	It is the sum of the powers of the concentration terms in the rate law expression.	It is the total number of reactant species collide simultaneously in a chemical reaction.
2.	It is an experimental quantity.	It is a theoretical quantity.
3.	It can be zero or fractional.	It cannot be zero or fractional.
4.	It is applicable to both elementary and complex reactions.	It is applicable only to elementary reactions.