Chemistry chapter 4 chemical kinetics # chemistry chapter 4 chemical kinetics # chemistry chapter 4 chemical kinetics # chemistry chapter 4 chemical kinetics # chemistry chapter 4 chemical kinetics pdf download # pdf download #pdf download #pdf download

1. Chemistry Video lecture series
CHEMICAL KINETICS
-By Shubham Mishra

2. CHEMICAL KINETICS
The father of chemical kinetics is L F Will Henry.
Kinetics=
𝐶ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛
𝑡𝑖𝑚𝑒
In chemistry distance is analogous to concentration.
Chemical Kinetics=
𝐶ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛
𝑡𝑖𝑚𝑒
The branch of physical chemistry that deals with the Rate of Reaction and Factors affecting
the rate of reaction
A+B C ; Rate=
𝑑
𝑑𝑇
=
𝐶ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛
𝑡𝑖𝑚𝑒
Conc [C] Rate=
∆𝐶
∆𝑇
[A]
time

3. CHEMICAL KINETICS
Rate of disappearance of A=
−𝑑𝐴
𝑑𝑇
Rate of disappearance of B=
−𝑑𝐵
𝑑𝑇
Rate of Appearance of C=
𝑑𝐶
𝑑𝑇
On the basis of rate of reaction. A reaction can be classified as:-
(i) Very fast reaction:- The completion time of such reaction lies between 10−12 to 10−14. Due to improper
knowledge of completion time. These are not Rate Determining Reaction. These are ionic reaction.
Ba𝐶𝑙2 + 𝐻2𝑆𝑂4 Ba𝑆𝑂4+2HCl
Ag𝑁𝑂3 + NaCl AgCl+ Na𝑁𝑂3
(ii)Moderate reaction:- The completion time of such reaction lies between very fast and very slow
reaction. Due to proper knowledge of their completion time. These are rate determining reaction.
𝐻2 + 𝐵𝑟2 2𝐻𝐵𝑟
P𝐶𝑙5 P𝐶𝑙3+ 𝐶𝑙2

4. (iii)Very slow reaction :-The completion time of such reaction maybe a month or year or a decade .Due
to improper knowledge of their completion time. These are not the rate determining reaction. These are
generally Molecular Reaction. . For example
• Reaction of 𝐶2 and 𝑂2 at room temperature.
• Reaction of 𝑁2 and 𝑂2 at room temperature.
• Reaction of 𝐻2 and 𝑂2 at room temperature .
• Formation of coal
• Rusting of iron
Stoichiometric Coefficient.
The coefficient of reactants and product In a balanced chemical reaction is known as stoichiometric
coefficient.
Eg:- 4A+5B 6C+5D
Ag𝑁𝑂3 + NaCl AgCl+ Na𝑁𝑂3
20𝐻2 + 20𝐵𝑟2 40𝐻𝐵𝑟
2𝑁2𝑂5 4N𝑂2 +𝑂2

5. Per Stoichiometry disappearance of any one of the reactant =Per Stoichiometry appearance of any one of the
product.
(i) A + B C + D
Initially T=0 a b 0 0
At temp T=t a-x b-x x x
(ii) 4A + 5B 6C + 7D
Initially T=0 a b 0 0
At temp T=t a-4x b-5x 6 x 7x
At temp T=t a-x b-5/4x 3/2 x 7/4x
(iii) 3A + 1/2B 5/2C + 3/2 D
Initially T=0 a b 0 0
At temp T=t a-3x b-1/2x 5/2x 3/2x

6. Rate of Reaction
Reaction rate, in chemistry, the speed at which a chemical reaction proceeds. It is often expressed in
terms of either the concentration (amount per unit volume) of a product that is formed in a unit of time or
the concentration of a reactant that is consumed in a unit of time.
Instantaneous rate :- Is the rate of a reaction at any particular point in time, a period of
time that is so short that the concentrations of reactants and products change by a negligible
amount. The initial rate is the instantaneous rate of reaction as it starts (as product just begins to
form).
𝑑𝐶
𝑑𝑇
=lim
𝑇→0
∆𝐶
∆𝑇

10. Factors Affecting The Rate Of Reaction
(i)Nature Of Reactant:-
Rate of Homogeneous reaction is greater than rate of Heterogeneous reaction.
A Homogeneous reaction is one in which all the reactant and product is present in same physical state.
Example:- (a) A(g) + B(l) C(l) RORI
A(g) + B(g) C(g) RORII
RORII>RORI
(b) 𝑁2 (g) + 3𝐻2 (g) 2N𝐻3 (g) RORI
𝑁2 (g) + 3𝐻2 (l) 2N𝐻3 (l) RORII
RORI>RORII
(II) Temperature:-
temperature increases kinetic energy increases number of Collision
increases number of active molecule increases rate of reaction

11. So this concludes that rate of reaction is directly proportional to temperature.
(III)Presence Of Catalyst :-
In the presence of catalyst activation energy decreases rate of reaction increases .
When Nature of catalyst is not given then it is common understanding that it is positive catalyst
which increases rate of reaction while negative catalyst decreases the rate of reaction.

12. (iv) Surface Area:-
combustion
combustion
So above we conclude that rate of reaction is directly proportional to surface area.
(i)Piece of coal burns faster than a lump of coal because of surface area
(II)Powder form of salt is more soluble than a lump of salt.

13. (v)CONCENTRATION:-
(v) Imposer Of Radiation :-
Rate of photochemical reaction depends on the intensity of radiation
C𝐻4 + 𝐶𝑙2 no reaction
𝐶𝐻4 + 𝐶𝑙2 ℎ𝑣 𝐶𝐻3𝐶𝑙 +HCl
for the reaction if I is the intensity of radiation
then rate of reaction of photochemical reaction is directly proportional to I
ROR∝ 𝐼 ROR= 𝐾𝐼 𝐾 equals to proportionality constant
So above we conclude that rate of reaction is directly proportional to concentration.
20% oxygen COMBUSTION
1000% oxygen COMBUSTION

14. IIT 2010:- AB hv A𝐵∗ for the reaction if I is the intensity of
radiation Bthen rate of reaction of photochemical reaction Is directly proportional to
(a)I
(b)CI
(c) I*I
(d) C*I*I

15. LAW OF MASS ACTION:-
Proposed By Guldberg Wage
According to mass action rate of reaction is directly proportional to concentration of reactant molecule
A Product
ROR ∝ [A]
If more than one reactant is present then rate of reaction is directly proportional to product of molar
concentration of reactant molecule.
A+B Product
ROR ∝ [A][B]
If stoichiometric coefficient is given then it is raised to the power.
aA + bB Product
ROR ∝ [𝐴]𝑎[𝐵]𝑏
ROR =K [𝐴]𝑎
[𝐵]𝑏
K is called the velocity constant or the rate constant or the specific rate constant

16. Rate Constant =Rate Of Reaction When The Concentration Of Each Reactant Molecule Is Taken Unity
aA + bB Product
ROR ∝ [𝐴]𝑎[𝐵]𝑏
ROR =K [𝐴]𝑎
[𝐵]𝑏
ROR =K [1]𝑎
[1]𝑏
ROR =K
The Rate constant equals to rate of reaction when the concentration of each reactant molecule is taken Unity
Characteristic Of Rate Constant Velocity Constant Specific Rate Constant
• Rate constant value depends on temperature
• Rate constant depends on nature of reactant
• Rate constant K depends on catalyst (positive catalyst increases the value of rate constant k)
• Rate constant K does not depend on concentration
• Rate constant of not depend on time
• Rate constant does not depend on value of container

17. NOTE :-By changing the volume of container concentration changes rate of reaction changes
• Rate constant does not depend on addition of inert gas
• Rate constant does not depend on degree of dissociation
• More the value of k faster the rate of reaction

18. (ii)Integrated form of Arrhenius equation:-
𝑑
𝑑𝑇
(log𝑒 𝐾)=
𝐸𝑎
𝑅𝑇2
By integrating the differential equation above w.r.t to dT we get:-
𝑑
𝑑𝑇
log𝑒 𝐾 dT =
𝐸𝑎
𝑅𝑇2
𝑑𝑇
By integrating the differential equation above w.r.t to dT we get:-
𝑑
𝑑𝑇
log𝑒 𝐾 dT =
𝐸𝑎
𝑅𝑇2
𝑑𝑇
log𝑒 𝐾 =
−𝐸𝑎
𝑅𝑇
+C where C is integration
constant
K=𝑒(
−𝐸𝑎
𝑅𝑇
+𝐶)
𝑒𝑥+𝑦
= 𝑒𝑥
∗ 𝑒𝑦

19. K=𝑒
−𝐸𝑎
𝑅𝑇 ∗ 𝑒𝐶
K=A*𝑒
−𝐸𝑎
𝑅𝑇 integrated form of Arrhenius equation
A=𝑒𝐶
Where A is Arrhenius parameter / pre exponential factor/frequency factor/collision
factor
-
−𝐸𝑎
𝑅𝑇
is called exponential term ; 𝑒
−𝐸𝑎
𝑅𝑇 =Boltzmann factor
• Its Dimensionless quantity
NOTE:UNIT OF A=UNIT OF K=𝑚𝑜𝑙(1−𝑛)𝑙𝑖𝑡𝑟𝑒(𝑛−1)𝑠𝑒𝑐−1
For:-
Zero order=𝑚𝑜𝑙(1)𝑙𝑖𝑡𝑟𝑒(−1)𝑠𝑒𝑐−1
First order=𝑠𝑒𝑐−1
Second order=𝑚𝑜𝑙(−1)
𝑙𝑖𝑡𝑟𝑒(1)
𝑠𝑒𝑐−1

20.  Case I:-If Ea=0;
Special Case Of Arrhenius Equation:-
K= A*𝑒
0
𝑅𝑇
K=A
 Case II:-If T ∞
K=A*𝑒
−𝐸𝑎
𝑅𝑇
K=A*𝑒
−𝐸𝑎
𝑅∗∞
K=A
 Ques.IIT.(2000):-In Arhenius equation K=A*𝑒
−𝐸𝑎
𝑅𝑇 K can be termed as A:
(a)Ea=∞ and T=0
(b)Ea=0 and T=∞
(c)Ea≠ 0 and T≠ 0
(d)Ea=0 and T=0

21. IIT 1996:- At 25℃ for a first order reaction K,A,and Ea are 3*104𝑠𝑒𝑐−1, 1*104𝑠𝑒𝑐−1
and 325 KJ/mol respectively then find the Rate Constant K AT Temperature T
ANS:-K=A= 1*104
𝑠𝑒𝑐−1
∞

22. T Ea/RT -Ea/RT K=𝐴 ∗ 𝑒
−𝐸𝑎
𝑅𝑇
From K=𝐴 ∗ 𝑒
−𝐸𝑎
𝑅𝑇 we have
• So from here we conclude that Rate constant value depends on temperature i.e. K∝ 𝑇
• By increasing Temperature K increases Exponentially.
K
TEPERATURE

23. K
TEPERATURE
IIT 2005:-In Arhenius Equation K=𝐴 ∗ 𝑒
−𝐸𝑎
𝑅𝑇 correct plot of K vs T is?
(A) (B)
(C) (D)
K
TEPERATURE
K K
TEPERATURE
TEPERATURE

24. Activation energy
Activation energy amount of energy required for the reactant molecule to form. The activated complex is
called. OR
Activation energy amount of energy below which the colliding molecule cannot form the product is called
activation energy.
Ea(Activation Energy)
Threshold energy
=Ea+Internal Energy ∆𝐻
Internal Energy
• +ive catalyst lowers the Activation energy Ea.
• -ive Catalyst increases the Activation energy Ea.

25. • Activation energy does not depend upon temperature.
• Activation energy does not depend upon Stoichiometry coefficient.
• Activation energy mainly depends upon catalyst
Catalyst Ea Ea/RT -Ea/RT K=A*𝑒
−𝐸𝑎
𝑅𝑇
+ive catalyst
-ive catalyst
• 2𝑁2𝑂5 4N𝑂2 +𝑂2 𝐸𝑎1
• 𝑁2𝑂5 2N𝑂2 +1/2𝑂2 Ea2
Ea1=Ea2(Activation Energy doesn’t depend on stoichiometric coefficient)

26. IIT 2000:-A hydrogenation reaction is carried out at 500 Kelvin if the same reaction is carried out in the
presence of catalyst with the same rate at 400 Kelvin. Calculator Ea for the same reaction if catalyst lowers the
activation energy by 20 KJ/mole.
SOLUTION:- Absence of catalyst Presence of Catalyst
T1 =500 K T2=400K
Ea1 = Ea Ea2=Ea-20
K1=K K2=K
K1=A*𝑒
−𝐸𝑎
𝑅∗500𝑘 K2=A*𝑒
−(𝐸𝑎−20)
𝑅∗400𝑘
K1=K2
A*𝑒
−𝐸𝑎
𝑅∗500𝑘=A*𝑒
−(𝐸𝑎−20)
𝑅∗400𝑘 𝑒
−𝐸𝑎
𝑅∗500𝑘 =𝑒
−(𝐸𝑎−20)
𝑅∗400𝑘 (Taking Log Both Side)
−𝐸𝑎
𝑅∗500𝑘
=
−(𝐸𝑎−20)
𝑅∗400𝑘
Solving this we get Ea=100KJ/mole