collision theory ppt help for learning ,also help for seminar type ,this ppt also helpful for chemical dynamics

1. Theories of chemical dynamics
SBRM govt. PG collEge ,nagaur
SEMINAR 2021-2022
SUBMITTED BY :-
MANJEET SINGH RAJAWAT
M.SC. Chemistry
Previous(sem. 1st )
SUBMITTED TO:-
DEPARTMENT OF CHEMISTRY
H.O.D. Dr. HARSHUKH CHHARANG
Collision Theories of Reaction Rates

2.  COLLISION THEORY OF REACTION RATES
• Manjeet singh rajawat
• Shree B.R. Mirdha College,nagaur
Introduction
Postulates
Terms based on collision theories
Factor affecting the effective collision
Mathematical representation
Derivation
Limitations
Reference

3.  This theory was proposed by “max troutz” and w.c.
lewis.
 This theory is based on the kinetic theory of gases
 According to which molecule of gases are in contiuous
in motion and hence collide with each other and
collision between these molecules in a certain way
produce product.
 Since for the collision at least two molecule are must
involved ,therefore this reaction is known as
bimolecular reaction .

4.  Reactant molecule is assume to be a hard sphere .
 For a successful reaction the collision must be
effective .
 the rate of collision frequency is quite high but rate of
product formation is not so .
 The number of collision that actually bring out the
chemical change ( yield product ) are known as
effective collision ,all the collision is not effective .

5. Threshold energy :-
Number density :-
the minimum amount of energy
that must be passes by the reactant molecule for the
effective collision is known as threshold energy.
This is generally denoted by = “ Ea”
Number of molecules per unite volume
is called number density.
This is generally denoted by = N*
Collision frequency :-
The number of collision that takes place per second per unit volume the
reaction mixture is called collision frequency
This is generally denoted by = Z

6. A. Energy barrier : -
B. orientation barrier : -
For a collision to be effective the colliding
molecule must posses a minimum amount of energy called
threshold energy .
For a collision to be effective the
collision must be properly orientated
For example -

7.  Collision theory is for bimolecular reaction because
for collision two molecules must be required .
 If the reaction molecule are not compressible and
molecular shape is spherical and identical then,
We can write that : -
d[R]
dt
Z.e-Ea/RT
Where Z = collision frequency
Ea = activation energy
T= temprature
………..(1)

8. d
A
VOLUME OF DISPLACED BY MOLECULE A = πσ d
2
distance in one second = ѵ
therefore d= v
Now volume swept out by molecule in one second = πσ ѵ
ѵ
2
* where σ =radius of molecule
A

9. NUMBER DENSITY (N*) : -
N* = N
V
Where
N = no. of molecule in the
container
V = volume of container
• Now how many molecules are there in volume = πσ ѵ
• Is = N πσ ѵ
• so collision frequency = πσ ѵ N*
• but this only valid when the molecule (A ) is moving and others
are stationary
•If we consider that the other molecules are also moving then the
velocity is become resultant velocity
2
V
2
2

10. • Resultant velocity in resultant θ = 90˚ ( in 0˚to 180˚)
• So that
• VR = v
• Collision frequency ZA = vπσ N*
• If we consider the collision of all molecule in 1 sec.
ZAA =
ZAA =
2
2
*
*
2 2 N
vN 

2
2
*)
(
2
N
v

2

11. • If two different types of molecules are present in the container
B
A
AB
AB
AB N
N
v
Z *
*
2


• where Zab = no. of collision in molecule A and B
• σab = σa + σb
• the SI unite of Zab = m s
• Now Rate of reaction according to collision theory =
q
Zab
RATE 

RT
Ea
B
A
AB
AB e
N
N
v
RATE

 .
*
*
2

According to rate of reaction
B
A N
N
K
RATE *
*
.

-3 -1

12. Now comparing both rate formulas gives
RT
Ea
ab
ab e
v
K

 .
2

m
kT
vab

8

We know that avg. velocity =
SO THAT we get: -
RT
Ea
AB e
kT
k

 .
]
8
[ 2
1
2



Where μ is reduced mass
Mb
Ma
1
1
1




13. Now comparision b/w arhenious factor and collision factor
Z= A
• For complex reaction the formula of ROR is
• Where P is a steric factor or probability factor
•For maximum of bimoleculare reaction steric factor have value less then
one .
RT
Ea
e
Zab
P
RATE

 .
.
.
.
CAL
EXP
K
K
P 

14.  This theory is applied only on a simple gases rxn. While
for complex reaction this theory is not applicable.
 For some reaction the rate of reaction given by collision
theory is differ from their experimental data .
In collision theory it is assume only str. of molecule is
elastic hard sphere like and structure aspect of molecule is
not taken.
Fail to calculate steric factor (p).
Collision theory is silent on breaking the bonds and
formation of the new bonds.
 collision theory assume molecule is elastic hard sphere
which is only true for the ideal gases.

15. 1. PURI SHERMA PATHANIA
46 th edition 2013
vishal publications
2. KEITH J. LAIDLER
CHEMICAL KINETICS
THIRD EDITION ,2018
published by p.i.e.s. pvt.ltd.