Definition of reaction kinetics, law of mass action, rates of reaction- zero, first, second, pseudo zero & pseudo first order reaction, molecularity of reaction, determination of reaction order- graphic method, substitution method, half life method.

1. Presented By:
Mahewash Sana A. Pathan

2.  Reaction kinetics
 Law of mass action
 Rate of reaction
 Molecularity of reaction
 Order of reaction
 Determination of reaction order

3.  “Chemical kinetics is the
branch of chemistry that is
concerned with understanding
the rates of chemical
reactions”
 In 1864, Peter waage and
Cato Guldberg pioneered the
development of chemical
kinetics by formulating law of
mass action.

4.  “ The rate of chemical reaction is
proportional to the product of the molar
concentration of the reactants each raised to
a power equal to the number of molecules of
the substance undergoing reaction.”
mA+ nB Product
Rate = K [A]m [B]n

5.  The speed or rate of a chemical reaction is
the change in concentration of a reactant or
product per unit time.
Rate = dc/dt

6.  Molecularity is number of molecules or atoms that
must collide to give products.
 Stoichiometric equation is essential to decide
molecularity.
 It must be small number & cannot be a fraction or
zero.
Molecularity of
reaction
Unimolecular Bimolecular Termolecular

7.  “Order of reaction is defined as the number of
concentration terms on which the rate of
reaction depends when determined
experimentally.”
OR
“ power dependence of the rate of reaction on the
concentration of each reactant.”
Types:
1. Zero order reaction
2. First order reaction
3. Second order reaction
4. Pseudo zero order reaction
5. Pseudo first order reaction

8.  A reaction in which the rate does not depend on the
concentration terms of the reactants.
-dc/dt = K0
Or
-dA/dt = K0
 E.g.
1. Colour loss of liquid multisulfonamide preparations
2. Oxidation of vit-A in oily solution
3. Photochemical degradation
of chlorpromazine

9.  A reaction in which the rate of reaction depends on
the concentration of one reactant.
-dc/dt = K1C
 E.g. decomposition of hydrogen peroxide catalysed
by KI.

10.  A reaction in which the rate depends on the
concentration terms of two reactants each
raised to the power one.
Rate= K2 [A] [B]
 E.g. Alkaline hydrolysis of esters, hydrolysis of
chlorbutanol

11.  A reaction which may be a first order but
behaves like a zero order, depending on
experimental conditions.
 E.g. Suspensions
-d[A]/dt = K1 [A]

12.  A reaction which is originally a second order
reaction but is made to behave like a first order
reaction.
 E.g.
1. Hydrolysis of ester catalyzed by H+ ions,
2. base catalyzed oxidative degradation of
prednisolone in aqueous solution
-dc/dt = K2 [A] [B]

13. 1. Graphic method
2. Substitution method
3. Half life method
4. Initial rate method
5. Software tools

14.  The kinetic experiment is conducted & data are
collected on the time course of changes in
concentration of reactants.
 A graph is plotted as per the general principles of
each reaction order.
 A straight line that gives best fit is identified, the
reaction is considered to be of that order.

15.  A kinetic experiment is conducted & data are
collected on the time course of changes in
concentration of reactants.
 Data are substituted in integral rate equations to
get K value.
 The order which gives constant K value at
different time periods within the experiment is
identified. The reaction is of that order.

16.  The half life are calculated for each time
period in the kinetic study.