2. Chemical Kinetics
Definition –
Study the rate of a chemical process..
Application
Drug Stability
Dissolution
Drug Release
Pharmacokinetics
Drug Action
3. Chemical Kinetics
Molecularirty of Reaction
In terms of a number which is equal to the
number of molecules that must collide
simultaneously to give product.
Types
Unimolecular Reactions
Bimolecular Reactions
Termolecular Reactions
5. Chemical Kinetics
Bimolecular Reaction
Same Type Molecule
Eg.. Oxidation Of Hydrogen Peroxide
2H2O2 2H2O + O2
Different Type molecule
CH3COOC2H5 + NaOH CH3COONa +C2H5OH
6. Chemical Kinetics
Order Of Reaction
As the number of concentration terms on which the
rate of reaction depends
Common order of reaction
Zero order
First order
Second order
Pseudo first order
7. Zero order Reaction
in which the rate of reaction does not
depend on the concentration terms of the reaction
-dc/dt=ko
Integral Equation..
Chemical Kinetics
8. Chemical Kinetics
Half life
Time required for the concentration of the
reactant to reduce to half of its initial concentration
t1/2 =a/2ko
Shelf life
Time required for the concentration of the
reactant to reduce to 90 % of its initial concentration
t90 = 0.1a/ko
9. Chemical Kinetics
First order Reaction
in which the rate of the reaction depend
on the concentration of one reactant.
Integral Equation-
10. Chemical Kinetics
Half life
Time required for the concentration of the
reactant to reduce to half of its initial concentration
t1/2 =0.693 / k1
Shelf life
Time required for the concentration of the
reactant to reduce to 90 % of its initial concentration
t90 = 0.105 / k1
11. Chemical Kinetics
Second order Reaction
in which the rate of the reaction depend
on the concentration of two reactant.
Integral Equation-
12. Chemical Kinetics
Half life
Time required for the concentration of the
reactant to reduce to half of its initial concentration
t1/2 = 1 / ak2
13. Chemical Kinetics
Pseudo First order Reaction
Reaction which is originally a second order but
is made to behave like a first order reaction.
16. Chemical Kinetics
Substitution Method
Conduct the kinetic experiment and collect the
data on time course and substitute the data in the
integral equations of order of reaction to get K values
Zero order
18. Chemical Kinetics
Half life method
Calculate the average k value using integral equation
of orders from substitution method. Then estimate
the t1/2 values by
19. Chemical Kinetics
In general the relationship between half life and
initial concentration are as follows
20. Chemical Kinetics
Conduct the experiment at two different initial
concentration called a1 and a2,then the half life
t1/2(1) and t1/2(2) are related as follows
Where n = Order of that reaction
21. Factors Influencing Reaction Rates
Temperature
The rate of reaction increases two or three times as
increase in 100 C Temp.
Arrhenius Equation
22. Factors Influencing Reaction Rates
Solvents
A polar solvent tends to increase the rate of those
reactions in which product formed is more polar
than reactants.
If the products are less polar then it tends to
decrease the rate of such reactions.
Commonly used non aqueous solvents for drugs
include Ethanol, Glycerol and vegetable oil etc.
23. Factors Influencing Reaction Rates
Ionic Strength
An increase in the ionic strength of solution would
tend to decrease the rate of reaction.
Because of the shielding effect of additional ions.
24. Factors Influencing Reaction Rates
Dielectric constant
The dielectric constant (or relative permittivity ) of
solvent has a significant effect on the rate of reaction.
If the reacting ions are of opposite charges then it
will result in increase rate of reaction.
If ions of similar charges involve in reaction it will
decrease rate of reaction.
25. Factors Influencing Reaction Rates
Catalysis
A catalyst is defined as a substance which increase or
decrease the rate of reaction without itself being
altered chemically.
Most of the chemical reactions are catalyzed in the
presence of catalyst.
These enhanced the rate of reaction by providing an
alternative course for chemical reaction.
