chemical kinetics studies

1. CHEMICAL KINETICS
STUDIES
Presented By-
ROHIT
R.K.S.D college of pharmacy, Kaithal (Hry)
M.Pharma 1st year
(Pharmaceutics)

2. CONTENTS
• Introduction
• Rates and order of reaction
• Method for determining the order of reaction
• Factor affecting rate of reaction
• kinetics of drugs decompositions
•Applications

3. Definition
Kinetics & Drug stability
•Drugs stability is defined as the pharmaceutical dosages form to
maintain the physical, chemical, therapeutic and microbial properties
during the time of storage and uses by the patient.
• Stability is defined as the capacity of a drugs substance to remain
within the established specification to maintain its identity, strength,
quality and purity throughout the retest or expiration during period.
•Chemical kinetics is the study of rate of chemical changes taking place
during chemical reaction.
Chemical kinetic:
Chemical kinetic involve the study of the rate of chemical process .
The rate of reaction can be understood by studying the time course
change in concentration.

4. RATES AND ORDER OF REACTION
The velocity with which a reaction or a process occurs is called as its
rate, concentration of drugs influences the rate of reaction or process is
called as the order of reaction or order of process.

5. The rate of forward reaction is expressed as :
-dA/dt
-ve sign = concentration of drugs A decreases with time.
As the reaction proceeds, the concentration of the drugs B increases
and the rate of reaction can also be expressed as:
dB/dt
Experimentally, the rate of reaction is determined by measuring the
decrease in concentration of drugs A with time.

6. If c is the concentration of drug A, the rate of decrease in c of drug A as
it is changed to B can be described by expression as function of time t.
dC/dt = -kcn (n is the power of concentration).
Where,
k= rate constant
n=order of reaction
If,
n= 0 (zero order process)

7. The order of a reaction determines the way in which the concentration
of a reactant or reactants influences the rate of a chemical reaction.
Molecularity of Reaction
The molecularity of a reaction refers to the numbers of molecules,
atoms, or ions reacting in a elementary process to give the reactants.
If only one type of molecules undergoes a change in to yield the
product , the product is said to be unimolecular.
If two molecules undergoes to change yield the product, the reaction is
said to be bimolecular.
Reaction that involves more than one steps ( complex reaction) may
have different molecularity and order of reaction.

8. The three commonly encountered rate process:
1. Zero order reaction
2. First order reaction
3. Second order reaction
Types of order of reaction

9. Zero-order kinetics
o Its is also called as constant rate process.
o The reaction is said to be zero-order reaction , if the rate of reaction is
independent of the concentration i.e. the rate of reaction can not be
increased further by increasing the concentration of reactants.
dc/dt= -KoCo = -Ko equation.....1
Where
Ko = zero-order rate constant (in mg/min)
Rearrangement of equation 1 yields:
dc= -Ko dt equation..........2
Integration of equation 2 gives:
C - Co = - k0 t
where
Co = concentration of drug at t = 0, and
C = concentration of drug yet to undergo reaction at time t.

11. First-order kinetics
Whose rate is directly proportional to the concentration of the of drugs
undergoing reaction i.e. greater the concentration , faster the reaction.
First-order process is said to follow linear kinetics
dC/dt= -KC
Where
K = first-order rate constant (per hour)

13. SECOND-ORDER REACTION
• the rate of reaction is directly proportional to the square of the
concentration of one of the reactants.
• r = k [A]2

14. Factor affecting rate of chemical
reaction
•Concentration of reactant
•Pressure
•Temperature
•Catalyst
•Nature of reactant
•Surface area
•Intensity of light
•Nature of solvent

22. Determination of Order of Reaction
• Use of rate equation – The data collected in a kinetic reaction should
be substituted into the integrated form of equations of various orders.
•The process under test should be considered to be of that order where
the calculated k value remains constant within limits of experimental
error.
•Half life method – For a zero order or pseudo first order reaction, t .
is proportional to initial concentration of reactant (Co), t. for a first order
reaction is independent of Co, .

23. Graphical method – For a zero order or pseudo first order
reaction, plot of C vs. t is linear; for first order reaction, plot of log (Co-
Ct) vs. t is linear.

24. Thank you