Kavita_Maheshwari semester 1

2. Chemical
kinetics
Date : 16 April1864
Info : Peter Waage and Cato
Guldberg pioneered the
development of chemical
kinetics by formulating the law
of mass action
Chemical kinetics is the study of chemical reactions with respect to
reaction rates, effect of various variables, rearrangement of atoms and
formation of intermediates. The study of chemical kinetics involve-
 Rate of reaction
 Factors affecting rate of reaction
 Mechanism of reaction

3. In chemistry, the rate of a chemical reaction, or the reaction rate, is
usually expressed as the change in the amount of reactant or product
per unit time.

4. Concentration
of solution
Temperature
Catalyst
Total surface
area
Pressure
FACTORS
AFFECTING
FACTORS AFFECTING RATE OF REACTION –

5. Reaction mechanism
The overall progress of a chemical reaction can be represented at the molecular level by
a series of simple elementary step or elementary reaction.
The sequence of elementary step that leads to product formation is the reaction of
mechanism.
Intermediate are species that appear in a reaction mechanism but not in the
overall balanced equation.

6. DO YOU KNOW ?
Why does milk rise up on
boiling, but water doesn't ?

7.  The minimum kinetic
energy a pair of traveling
particles must have when
they collide.
 The minimum energy
that colliding particles
must have in order to
react is called the
activation energy.
,
THRESHOLD ENERGY & ACTIVATION ENERGY

8. Arrhenius Equation
Temperature dependence of rate constants is described by Arrhenius equation.
Ea= Activation energy and is given by the
energy difference between activated complex
and the reactant molecules.
Measured in joules/mole (J mol–1).
A =(Arrhenius factor or pre-exponential factor)
corresponds to the collision frequency.
R= gas constant

9. Transition State Theory
It provides a simple and useful
way to understand and determine
the rate coefficients of chemical
reactions. It was first proposed
by Eyring [103] and Evans-
Polanyi [104] in 1935.
3
Arrhenius theory
Arrhenius theory, theory,
introduced in 1887 by the
Swedish scientist Svante
Arrhenius
2
Collision Theory
A model called collision theory is
used to relate the properties of
particles to the rates of chemical
reactions. Given by William Lewis
and Max Trauntz in 1916.
1
Theories of reaction rate -

11. Effective and ineffective collision

12. Transition State Theory
o This theory also known as absolute rate complex or
activated complex theory.
o This theory includes thermodynamic conditions in the rate
of reaction.
o The energy of transition state is higher than reactant
molecules as well as product molecules.
o The transition state exist in fast equilibrium with reactant
molecules.

13. ACTIVATED COMPLEX
 An activated complex is an unstable
arrangement of atoms that forms for a
moment at the peak of the activation-
energy barrier.
 The activated complex forms only
if the colliding particles have
enough energy and if the atoms
are oriented properly.
 The activated complex
is sometimes called
the transition state.

14. Collision Theory
 The reactant molecule collide each
other to form products.
 This theory is applicable only for
bimolecular gaseous reaction.
 This include activation energy and
doesn’t include rotational and
vibrational energy.
 It doesn’t define steric factor.
Transition State Theory
 Reactant molecules form transition state
for activated complex before formation
of product.
 This theory is applicable for
unimolecular , bimolecular, and
trimolecular process also.
 This theory can be applied to reactions
in a solution whereas collision theory is
applicable for gaseous reactions.
COMPARISON

15. ARRHENIUS THEORY

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Reference and
Notes
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