SANKALP EDUCATION

CLASS- 12

Physical Chemistry
Unit – CHEMICAL KINETICS
Part - 1
Class - XII Topic : Chemical Kinetics
 Chemical Kinetics ¼jklk;fud xfrdh½
Kinesis is a Greek word.
Kinesis ,d xzhd 'kCn gSA
It means movement.
bldk eryc xfr gksrh gSA
A branch of physical chemistry.
HkkSfrd jlk;u dh og 'kk[kkA

Class - XII Topic : Chemical Kinetics

 Which deals with ftlesa fdlh
Rate of a chemical reaction, izfrfØ;k ds nj
Its factors izHkkfor
djus okys dkjd
Its mechanism. mlds mechanism

This is called chemical kinetics.

jklk;fud xfrdh dgrs gSaA

Class - XII Topic : Chemical Kinetics

 Chemical Kinetics
Rate of a chemical reaction.
izfrfØ;k dh njA
Factors of a chemical reaction.
izfrfØ;k dks izHkkfor djus dh dkjdA
Time to complete a reaction.
izfrfØ;k dks iw.kZ gksus esa yxk le;A
Mechanism of a chemical reaction.
fdlh jklk;fud izfrfØ;k ds iw.kZ gksus dk fooj.kA
Class - XII Topic : Chemical Kinetics
 In Chemistry there are changes in which a
substance is converted into another
substance.
jlk;u'kkL= esa ,d inkFkZ dk ifjoÙkZu nwljs inkFkZ esa
gksrk gSA
converted
Substance – I Substance - II

converted
Reactant Product
izfrdkjd izfrQy

Class - XII Topic : Chemical Kinetics

 converted
Reactant Product
izfrdkjd izfrQy
NH4NO2 N2 + 2H2O

2H2O2 2H2O + O2

N2O5 N2O4 + ½O2

Class - XII Topic : Chemical Kinetics

 Chemical reaction has three parameters
jklk;fud lehdj.k ds rhu vo;o gksrs gSa

Thermodynamic parameter
m"ekxfrdh dkjd

Chemical equilibrium
jklk;fud lkE;koLFkk

Chemical Kinetics
jklk;fud xfrdh
Class - XII Topic : Chemical Kinetics
 Feasibility of a reaction ¼izfrfØ;k laHkkfor½

Thermodynamics parameter
G < 0 (negative) at constant temperature.
Gibb’s free energy change is negative

fdlh jklk;fud izfrfØ;k ds fy, ;fn Lora= ÅtkZ

dk eku fu;r rki ij ;fn _.kkRed gks rks og
izfrfØ;k Lor% gksxhA

Class - XII Topic : Chemical Kinetics

 Chemical equilibrium

To what extent a reaction takes place –

chemical equilibrium.
jklk;fud lkE;koLFkk fdlh izfrfØ;k ds gksus ds
Lrj dks n'kkZrk gSA
Conditions for maximum yield
egÙke izfrQy dh izkfIr ds 'krZA

Class - XII Topic : Chemical Kinetics

 Classification of
reaction

On the basis of
rate of a reaction
Class - XII Topic : Chemical Kinetics
 Rate of a Chemical Reaction
jklk;fud izfrfØ;k dh nj
On the basis of rate of reaction, reactions are
classified into three parts.
izfrfØ;k dh nj ds vk/kkj ij lehdj.k dks rhu Hkkxksa esa
oxhZd`r fd;k tkrk gSA

Class - XII Topic : Chemical Kinetics

 1. Very Fast Reaction ¼rkRdkfyd izfrfØ;k½

A reaction which is completed instantaneously.

It means it takes very small time less than or
equal to 10-12 sec.
og izfrfØ;k ftls iw.kZ gksus esa dkQh de le; yxrk gS
vFkkZr 10-12 second ;k mlls Hkh de le; yxrk gS]
rkRdkfyd izfrfØ;k dgykrk gSA

Class - XII Topic : Chemical Kinetics

 2. Very Slow Reaction ¼vfrean izfrfØ;k½
A reaction which is completed in very long time
is called very slow reaction.
og izfrfØ;k ftls iw.kZ gksus esa dkQh vf/kd le; yxrk gS]
vfrean izfrfØ;k dgykrk gSA

Class - XII Topic : Chemical Kinetics

 3. Moderate Reaction ¼ean izfrfØ;k½
A reaction which has rate of reaction between
very fast and very slow reaction is called
moderate reaction.
og izfrfØ;k ftls iw.kZ gksus esa yxk le; rhoz izfrfØ;k ls
vf/kd rFkk vfr ean izfrfØ;k ls de le; yxrk gSA

Class - XII Topic : Chemical Kinetics

 Most of the chemical reactions are moderate
reactions.
T;knkrj jklk;fud vfHkfØ;k ean vfHkfØ;k,¡ gksrh gSA

The rate of reaction is practically consider for

moderate reaction.
fdlh izfrfØ;k dh nj dh x.kuk T;knkrj izfrfØ;k ds
fy, djrs gSaA

Class - XII Topic : Chemical Kinetics

 Molar concentration
eksyj lkUnzrk = eksyjrk
Number of moles of solute (substance) present in
one litre of solution is called molar concentration.
fdlh ?kksy ds ,d fyVj esa ?kqY; ds eksy dh la[;k dks
eksyjrk dgrs gSaA

Class - XII Topic : Chemical Kinetics

 Symbol = [ ] or C
ladsr = [ ] or C

n Mole
C = V = litre = mole litre-1 or M

eksy dh la[;k
C = = eksy fyVj-1
vk;ru
= M

Class - XII Topic : Chemical Kinetics

 Example ¼mnkgj.k½

Molar concentration of A = [A]

A dh eksyj lkUnzrk = [A]

Molar concentration of B = [B]

B dh eksyj lkUnzrk = [B]

Class - XII Topic : Chemical Kinetics

 Example ¼mnkgj.k½
Molar concentration of NH3 = [NH3]

NH3 dh eksyj lkUnzrk = [NH3]

Molar concentration of NO = [NO]

NO dh eksyj lkUnzrk = [NO]

Class - XII Topic : Chemical Kinetics

 Example ¼mnkgj.k½

R P

Molar conc. of Reactant = [R]

Reactant dh eksyj lkUnzrk = [R]

Molar conc. of Product = [P]

Product dh eksyj lkUnzrk = [P]

Class - XII Topic : Chemical Kinetics

 Rate of reaction
izfrfØ;k dh nj
Rate of reaction w.r.t. reactant
izfrfØ;k dh nj izfrdkjd ds lkis{k

Class - XII Topic : Chemical Kinetics

 R P

Experiment - 1 Experiment - 2

R1 =100
R2 = 80

P1=0 P2=20
P1 P2

Class - XII Topic : Chemical Kinetics

 Rate of reaction w.r.t. reactant
izfrfØ;k dh nj izfrdkjd ds lkis{k
R P
Time = t1 = 0

Initial Conc. [R1] = 100

Time = t2 = 10

Final Conc. [R2] = 80

Class - XII Topic : Chemical Kinetics
 Change in conc. = [R] = [R2] – [R1]
lkUnzrk esa ifjoÙkZu
Change in time interval = t = t2 – t1
le; varjky esa ifjoÙkZu
Rate of reaction w.r.t. reactant
izfrdkjd ds lkis{k izfrfØ;k dh nj
[R] [R2] – [R1] 80 – 100 20
= = = = -2
t t2 – t1 10 – 0 10

Class - XII Topic : Chemical Kinetics

 Rate of reaction izfrfØ;k dh nj

[R]
r = = -2
t
Multiplying both sides by – 1

[R]
r = = - (-2)
t
[R]
r = =+2
t
Class - XII Topic : Chemical Kinetics
 1.R 1.P
Rate of decrease of Reactant
izfrdkjd ds deh dh nj

Rate of disapprearence of Reactant [R]

izfrdkjd ds ?kVus dh nj t

Rate of consumption of Reactant

izfrdkjd ds [kir dh nj
Class - XII Topic : Chemical Kinetics
 Rate of reaction
izfrfØ;k dh nj

Rate of reaction w.r.t. product

izfrfØ;k dh nj izfrQy ds lkis{k

Class - XII Topic : Chemical Kinetics

 Rate of reaction w.r.t. product
izfrfØ;k dh nj izfrQy ds lkis{k

R P

Time = t1 = 0 [P1] = 0 Initial Conc.

Time = t2 = 10 [P2] = 20 Final Conc.

Class - XII Topic : Chemical Kinetics

 Change in conc. = [P] = [P2] – [P1]
lkUnzrk esa ifjoÙkZu
Change in time interval = t = t2 – t1
le; varjky esa ifjoÙkZu
Rate of reaction w.r.t. product
izfrQy ds lkis{k izfrfØ;k dh nj
[P] [P2] – [P1] 20 – 0 20
= = = = +2
t t2 – t1 10 – 0 10

Class - XII Topic : Chemical Kinetics

 Rate of reaction izfrfØ;k dh nj
[R]
= -2
t

[P]
= +2
t

[R] [P]
r= =
t t

Class - XII Topic : Chemical Kinetics

 Rate of reaction [ Macroscopic level ]
Rate of consumption of reactant or Rate of
formation of product.
jklk;fud xfrdh dk o`gr Lrj ;g crkrk gS fd fdl
nj ij izfrdkjd dh lkUnzrk de gksrh gS rFkk izfrQy
dh lkUnzrk esa o`f) gksrh gSA

R P

Class - XII Topic : Chemical Kinetics

 1.R 1.P

Rate of reaction izfrfØ;k dh nj

[R] [P]
r= =
t t

Class - XII Topic : Chemical Kinetics

 1.R 1.P
Rate of appearence or increase or formation of
product
izfrQy ds izdV gksus dh nj ;k o`f) ;k fuekZ.k dh nj
=

[Product] [ izfrQy ] [P]

+ t = + = +
le; varjky t

Class - XII Topic : Chemical Kinetics

 Unit of rate of a reaction
izfrfØ;k dh nj dk ek=d

Class - XII Topic : Chemical Kinetics

 Unit of rate of a reaction
izfrfØ;k dh nj dk ek=d
R P
C Change in concentration
=
t Time interval

C lkUnzrk esa ifjoÙkZu

=
t le; varjky
= Mole litre-1 sec-1 or M sec-1
Class - XII Topic : Chemical Kinetics
 Unit of rate of a reaction
izfrfØ;k dh nj dk ek=d

A B
P Change in pressure
=
t Time interval

P nkc esa ifjoÙkZu

=
t le; varjky
= atm sec-1
Class - XII Topic : Chemical Kinetics
 SANKALP EDUCATION
CLASS- 12

Physical Chemistry
Unit – CHEMICAL KINETICS
Lecture – 1 completed
Class - XII Topic : Chemical Kinetics
 Law of mass action
nzO;eku lfØ;rk dk fu;e

Graph of rate of reaction

izfrfØ;k dh nj dk xzkQ

Sign in rate of reaction

izfrfØ;k dh nj dk fpUg

Class - XII Topic : Chemical Kinetics

 Graph of rate of a
reaction w.r.t. reactant

izfrdkjd ds lkis{k
izfrfØ;k dh nj dk xzkQ

R P

Class - XII Topic : Chemical Kinetics

 Rate of a Reaction w.r.t of Reactant

izfrdkjd ds lkis{k izfrfØ;k dh nj

Initially the rate of reaction w.r.t reactant is

maximum
izfrfØ;k dh nj izfrdkjd ds lkis{k izkjafHkd voLFkk
esa egÙke gksrh gSA

Class - XII Topic : Chemical Kinetics

 Reason ¼dkj.k½
The concentration of reactant is maximum
initially.
izkjafHkd voLFkk esa izfrdkjd dh lkUnzrk egÙke gksrh gSA
As time Progresses

The concentration of reactant decreases w.r.t

time.
le; ds lkFk izfrdkjd dh lkUnzrk esa deh vkrh gSA

Class - XII Topic : Chemical Kinetics

 The rate of conversion of reactant into
product is not uniform.
bldk rkRIk;Z ;g gksrk gS fd izfrdkjd dk
ifjoÙkZu izfrQy esa leku ugha gksrk gSA

Hence the graph between concentration of

reactant w.r.t. time is
vr% izfrdkjd ds lkis{k lkUnzrk rFkk le; ds chp
dk xzkQ

Class - XII Topic : Chemical Kinetics

 Graph of conc. Vs time w.r.t reactant
izfrdkjd ds lkis{k lkanzrk rFkk le; dk xzkQ
Y

C1
Concentration

C2
C3

X
O t1 t2 t3 time

Class - XII Topic : Chemical Kinetics

 Graph of Concentration
vs time w.r.t. product
izfrQy ds lkis{k lkanzrk
rFkk le; dk xzkQ
R P

Class - XII Topic : Chemical Kinetics

 Rate of reaction w.r.t of product
izfrQy ds lkis{k izfrfØ;k dh nj

The rate of reaction w.r.t product is zero

initially.
izfrfØ;k dh nj izfrQy ds lkis{k esa izkjafHkd
voLFkk esa 'kqU; gksrh gSA

Class - XII Topic : Chemical Kinetics

 Reason ¼dkj.k½
The concentration of product is initially zero.
All concentrations are in the form of
reactant.
izkjafHkd voLFkk esa izfrQy dh lkUnzrk 'kqU; gksrh gSA
lHkh lkUnzrk izfrdkjd ds :Ik esa jgrh gSA

The rate of reaction w.r.t product increases

with time.
izfrfØ;k dh nj izfrQy ds lkis{k le; ds lkFk
c<+rh gSA
Class - XII Topic : Chemical Kinetics
 The rate of reaction w.r.t product is not
uniform.
izfrfØ;k dh nj izfrQy ds lkis{k ges'kk leku ugha
jgrh gSA
Hence the correct nature of graph between
concentration of product w.r.t time is
vr% izfrQy ds lkis{k lkUnzrk rFkk le; ds chp dk
lgh xzkQ ;g gksrk gSA

Class - XII Topic : Chemical Kinetics

 Graph of concentration vs time w.r.t product

Lkkanzrk rFkk le; ds lkis{k izfrQy dk xzkQ

C3
Concentration

C2
C1

O X
t1 t2 t3 time

Class - XII Topic : Chemical Kinetics

 Sign of rate of a
reaction w.r.t. reactant
izfrdkjd ds lkis{k izfrfØ;k
dh nj dk fpUg

R P

Class - XII Topic : Chemical Kinetics

 Rate of reaction w.r.t Reactant
izfrdkjd ds lkis{k izfrfØ;k dh nj
Let a reaction ekuk fd
Reactant (R) is converted into product.
,d izfrdkjd (R) dk ifjoÙkZu izfrQy (P) esa gksrk gSA

R P

Class - XII Topic : Chemical Kinetics

 The concentration of reactant is [R]1 at time t1
and concentration of reactant is [R]2 at time t2.
ekuk fd t1 le; esa izfrdkjd dh lkUnzrk [R]1 ,oa
t2 le; esa izfrdkjd dh lkUnzrk [R]2 gks tkrh gSA

Class - XII Topic : Chemical Kinetics

Rate of disappearance or decrease or
consumption of reactant [R] =
izfrdkjd [R] ds ?kVus ;k deh gksus ;k [kir gksus dh nj
[R] [R2] – [R1] 80 – 100 -20
= = =
t t2 – t1 10 - 0 10
[R]
= -2
t
Multiplying both sides by – 1
nksuksa rjQ – 1 ls xq.kk djus ij

Class - XII Topic : Chemical Kinetics

Rate of decrease in concentration of reactant (R)
izfrdkjd ds lkis{k izfrdkjd esa deh dh nj
[R]
= - = +2
t

Class - XII Topic : Chemical Kinetics

 The value of rate of decrease of reactant [R]
is negative.

izfrdkjd ds lkis{k izfrfØ;k dh nj dk eku

_.kkRed gksrk gSA
Reason – Due to decrease in concentration of
reactant.

dkj.k & izfrdkjd dh lkUnzrk esa deh gksrh gSA

Class - XII Topic : Chemical Kinetics

 Negative sign (-ve) means decrease in
concentration of reactant with respect to
time.
fdlh izfrdkjd esa _.kkRed fpUg dh mifLFkfr dk
rkRIk;Z mldh izfrfØ;k dh nj esa le; ds lkis{k
deh gksrh gSA

Class - XII Topic : Chemical Kinetics

 1.R 1.P
Rate of decrease of Reactant
izfrdkjd ds deh dh nj

Rate of disapprearence of Reactant [R]

izfrdkjd ds ?kVus dh nj t

Rate of consumption of Reactant

izfrdkjd ds [kir dh nj
Class - XII Topic : Chemical Kinetics
 Sign of rate of a
reaction w.r.t. product
izfrQy ds lkis{k izfrfØ;k
dh nj dk fpUg
R P

Class - XII Topic : Chemical Kinetics

 Rate of reaction w.r.t Product
izfrQy ds lkis{k izfrfØ;k dh nj
Let a reaction ekuk fd
Reactant (R) is converted into product.
,d izfrdkjd (R) dk ifjoÙkZu izfrQy (P) esa gksrk gSA

R P

Class - XII Topic : Chemical Kinetics

 The concentration of product is [P1] at time t1
and concentration of product is [P2] at time
t 2.
ekuk fd t1 le; esa izfrQy dh lkUnzrk [P1] rFkk t2
le; esa izfrQy dh lkUnzrk [P2] gks tkrh gSA

Class - XII Topic : Chemical Kinetics

 Rate of appearance or increase or formation of
product [P] =
izfrQy [P] ds c<+us ;k o`f) gksus ;k izdV gksus dh nj

[P] [P2] – [P1] 20 – 0 20

= = = =2
t t2 – t1 10 - 0 10

Class - XII Topic : Chemical Kinetics

 The value of rate of increase of product [P]
is positive
izfrQy ds lkis{k izfrfØ;k dh nj dk eku /kukRed
gksrk gSA
Reason – Due to increase in concentration
of product.
dkj.k & izfrQy dh lkUnzrk esa o`f) gksrh gSA

Class - XII Topic : Chemical Kinetics

 Positive sign (+ve) means increase in
concentration of product with respect to
time.
fdlh izfrQy ds lkis{k izfrfØ;k dh dk eku
/kukRed gksrk gS ftldk dkj.k izfrQy dh
lkUnzrk esa o`f) gksrh gSA

Class - XII Topic : Chemical Kinetics

 1.R 1.P

Rate of increase of product

izfrQy ds o`f) dh nj [P]
+
t
Rate of apprearence of product
izfrQy ds izdV gksus dh nj

Rate of formation of product

izfrQy ds fuekZ.k dh nj
Class - XII Topic : Chemical Kinetics
 Rate of reaction having different
coefficients of reactant and products
izfrfØ;k dh nj ftlesa izfrdkjd rFkk izfrQy ds
fHkUu & fHkUu xq.kd gksrs gSaA

Class - XII Topic : Chemical Kinetics

 N2 + 3H2 2NH3
Rate of decrease of N2
ukbVªkstu ds deh dh nj

Rate of consumption of N2 [N2]

ukbVªkstu ds [kir dh nj t

Rate of disappearance of N2
ukbVªkstu ds xk;c gksus dh nj

Class - XII Topic : Chemical Kinetics

 N2 + 3H2 2NH3
Rate of decrease of H2
gkbMªkstu ds deh dh nj
[H2]
Rate of consumption of H2
t
gkbMªkstu ds [kir dh nj

Rate of disappearance of H2
gkbMªkstu ds xk;c gksus dh nj

Class - XII Topic : Chemical Kinetics

 N2 + 3H2 2NH3
Rate of increase of NH3
vuksfu;k ds o`f) dh nj

Rate of formation of NH3 [NH3]

+
veksfu;k dh nj t

Rate of appearence of NH3

veksfu;k ds gksus dh nj

Class - XII Topic : Chemical Kinetics

 Formation of NH3 ¼veksfu;k dk fuekZ.k½
1.N2 + 3.H2 2.NH3
Initial a b 0
moles
-x - 3x + 2x
Left
a-x b – 3x 2x
moles

Class - XII Topic : Chemical Kinetics

 Formation of Ammonia ¼veksfu;k dk fuekZ.k½

1.N2 + 3.H2 2.NH3

Rate of increase of NH3

Rate of decrease of N2

Rate of decrease of H2
-1 -3
-1 -3
-1 -3
-1 -3 +2
+2
+2
+2

Class - XII Topic : Chemical Kinetics

 Reactant izfrdkjd Product izfrQy

N2 + 3H2 2NH3

Rate of decrease of N2 [N2]

=1
ukbVªkstu ds deh dh nj t

Class - XII Topic : Chemical Kinetics

 Reactant izfrdkjd Product izfrQy

N2 + 3H2 2NH3

Rate of decrease of H2 [H2]

=3
gkbMªkstu ds deh dh nj t

Class - XII Topic : Chemical Kinetics

 Reactant izfrdkjd Product izfrQy

N2 + 3H2 2NH3
Rate of increase of NH3 [NH3]
+ =2
veksfu;k ds o`f) dh nj t

Class - XII Topic : Chemical Kinetics

 [N2]
- =1 ---------- (i)
t

[H2]
- =3 ---------- (ii)
t

[NH3]
+ =2 ---------- (iii)
t

Class - XII Topic : Chemical Kinetics

 Eq.(i) 1 lehdj.k (i) dks 1 ls Hkkx nsus ij
1 [N2] 1
- = =1
1 t 1
Eq.(ii) 3 lehdj.k (ii) dks 3 ls Hkkx nsus ij
1 [H2] 3
- + = =1
3 t 3
Eq.(iii) 2 lehdj.k (iii) dks 2 ls Hkkx nsus ij
1 [NH3] 2
+ = =1
2 t 2
Class - XII Topic : Chemical Kinetics
 Rate of reaction (izfrfØ;k dh nj) = r =

1 [N2] 1 [H2] 1 [NH3]

r = - =- = +
1 t 3 t 2 t

Class - XII Topic : Chemical Kinetics

 A reaction having different coefficient of
reactants and products
a.A b.B
Rate of decrease of A = [A]
A ds ?kVus dh nj = t

Rate of increase of B = [B]

+
B ds c<+us dh nj = t

Rate of reaction = r =
1 [A] 1 [B]
=+
a t b t
izfrfØ;k dh nj
Class - XII Topic : Chemical Kinetics
 Rate of reaction w.r.t reactant
izfrfØ;k dh nj izfrdkjd ds lkis{k
Rate of reaction ¼izfrfØ;k dh nj½ =

-1 [Reactant]
= x
Coefficient t

1 [izfrdkjd]
= - x
xq.kd le; varjky

Class - XII Topic : Chemical Kinetics

 Rate of Reaction w.r.t product
izfrfØ;k dh nj izfrQy ds lkis{k
Rate of reaction ¼izfrfØ;k dh nj½ =

+1 [Product]
= x
Coefficient t

1 [izfrQy]
= + x
xq.kd le; varjky

Class - XII Topic : Chemical Kinetics

 Rate of Reaction -
Definition
izfrfØ;k dh nj dh ifjHkk"kk

Class - XII Topic : Chemical Kinetics

 Rate of a Chemical Reaction ¼izfrfØ;k dh nj½
In a balanced chemical reaction.
fdlh larqfyr jklk;fud izfrfØ;k esa
Rate of disappearance of a reactant.
izfrdkjd ds deh dh njA
Divided by its stoichiometric coefficient.
ml izfrdkjd ds xq.kd ls Hkkx fn;k tk;A
This is called rate of reaction.
;g bl izfrfØ;k dh nj dgykrh gSA

Class - XII Topic : Chemical Kinetics

 Rate of a Chemical Reaction ¼izfrfØ;k dh nj½
In a balanced chemical reaction.
fdlh larqfyr jklk;fud izfrfØ;k esa
Rate of appearance of a product.
izfrQy ds o`f) dh njA
Divided by its stoichiometric coefficient.
ml izfrQy ds xq.kd ls Hkkx fn;k tk;A
This is called rate of reaction.
;g bl izfrfØ;k dh nj dgykrh gSA
Class - XII Topic : Chemical Kinetics
 Points
It is the measurement of decrease in
concentration of reactant or increase in
concentration of product in unit time.
;g bdkbZ le; esa izfrdkjd dh lkUnzrk esa deh rFkk
izfrQy dh lkUnzrk esa o`f) dks n'kkZrk gSA

Class - XII Topic : Chemical Kinetics

 Rate of reaction depends on initial
concentration of reactant
izfrfØ;k dh nj mlds izfrdkjd ds izkjafHkd lkUnzrk ij
fuHkZj djrk gSA
It has unit mole litre–1sec–1 or atm sec-1
izfrfØ;k dh nj dk ek=d mole litre–1sec–1 or atm
sec-1 gksrk gSA
Unit of rate of reaction does not depend on
order of reaction.
izfrfØ;k dh nj dk ek=d mlds dksfV ij fuHkZj ugha
djrk gSA
Class - XII Topic : Chemical Kinetics
 Rate of reactions are two types
izfrfØ;k dh nj nks izdkj dh gksrh gS

Average rate of reaction (rav)

vkSlr izfrfØ;k dh nj

Instantaneous rate of reaction (rInst)

rkRdkfyd ;k rkR{kf.kd izfrfØ;k dh nj
Class - XII Topic : Chemical Kinetics
 Average rate of reaction (rav)

vkSlr izfrfØ;k dh nj

Class - XII Topic : Chemical Kinetics

 1.R 1.P
t1 = Initial time C1 = Initial conc.
t1 = izkjafHkd le; C1 = izkjafHkd lkUnzrk

t2 = Final time C2 = Final conc.

t2 = vafre le; C2 = vafre lkUnzrk

Class - XII Topic : Chemical Kinetics

 Average rate of reaction = rav
vkSlr izfrfØ;k dh nj = rav

1.R 1.P

[R] [R2] – [R1]

rav = – = t2 – t1
t

Class - XII Topic : Chemical Kinetics

 [P] [P2] – [P1]
rav = = = +ve
t t2 – t1

Change in conc. [P]

rav = =
Change in time t

[R] [P]
rav = – = +
t t

Class - XII Topic : Chemical Kinetics

 Average rate of reaction w.r.t reactant

Concentration
C1
C2

O t1 t2 X

Class - XII Topic : Chemical Kinetics

 Average rate of reaction w.r.t Product

Concentration
C2
C1

O X
t1 t2

Class - XII Topic : Chemical Kinetics

 Average rate of reaction (rav)
vkSlr izfrfØ;k dh nj
Average rate of reaction is the decrease in
concentration of reactant or increase in
concentration of product in a definite time
interval.
fdlh jklk;fud izfrfØ;k esa fdlh fuf'pr le; varjky esa
izfrdkjd dh lkUnzrk esa deh ;k izfrQy dh lkUnzrk esa
o`f) dks vkSlr izfrfØ;k dh nj dgrs gaSA

Class - XII Topic : Chemical Kinetics

 Average rate of reaction gives information
about the rate of reaction in a particular time
interval. It has definite value in time interval.
vkSlr izfrfØ;k dh nj fdlh izfrfØ;k ds fy, fuf'pr
le; varjky esa lkUnzrk ds ifjoÙkZu dks n'kkZrk gSA
bldk eku fuf'pr le; varjky ds fy, fu;r gksrk
gSA

Class - XII Topic : Chemical Kinetics

 Points

It is the average value of rate of

reaction in the time interval
;g fuf’pr le; varjky ds vkSlr nj dks n’kkZrk gSA
It has definite value.
bldk eku fuf’pr gksrk gSA

Class - XII Topic : Chemical Kinetics

 Instantaneous rate of
reaction (rInst)

rkRdkfyd ;k rkR{kf.kd
izfrfØ;k dh nj

Class - XII Topic : Chemical Kinetics

 Instantaneous rate of reaction (rInst)

rkRdkfyd ;k rkR{kf.kd izfrfØ;k dh nj

At a particular instant (or moment) of time
fdlh fuf'pr le; ijA

The rate of decrease in concentration of

reactant
izfrdkjd dh lkUnzrk esa deh dh nj A

Class - XII Topic : Chemical Kinetics

 The rate of increase in concentration of
product.
izfrQy dh lkUnzrk esa o`f) dh nj A
It is called instantaneous rate of reaction.
bls rkR{kf.kd izfrfØ;k dh nj dgrs gSaA

Class - XII Topic : Chemical Kinetics

 Points
It changes at each instant of
time.
rkR{kf.kd izfrfØ;k dh nj ifjofÙkZr gksrh gSA
It is always variable.
bldk eku ifjoÙkZu”khy gksrk gSA

Class - XII Topic : Chemical Kinetics

 Graph w.r.t. reactant – Conc. Vs time
Y
C

O X
t
Class - XII Topic : Chemical Kinetics
 Graph of product – Conc. Vs time

Y
C

X
O t

Class - XII Topic : Chemical Kinetics

 Rate of a particular chemical reaction at any
instant of time is called Instantaneous rate of
reaction .
fdlh jklk;fud izfrfØ;k esa fdlh fuf'pr le; ij
izfrfØ;k dh nj rkRdkfyd ;k rkR{kf.kd izfrfØ;k dh
nj dgykrh gSA

Class - XII Topic : Chemical Kinetics

 Rate of a reaction at any time = slope of
tangent drawn at any point of time of
concentration vs time graph at a particular
time
fdlh izfrfØ;k esa fdlh fuf'pr le; ij lkUnzrk rFkk
le; ds chp [khps x, xzkQ ij fuf'pr le; ds fy,
Mkyk x;k tangent dk <+ky gh rkRdkfyd ;k rkR{kf.kd
izfrfØ;k dh nj dgykrk gSA

Class - XII Topic : Chemical Kinetics

 r = Slope of the tangent drawn

[R] dR
Rate of reaction = Lt [t] = dt
t0

Class - XII Topic : Chemical Kinetics

 Lecture - Topic
Factors affecting rate
of reaction

Rate of reaction

Class - XII Topic : Chemical Kinetics

 Factors affecting rate of reaction
izfrfØ;k dh nj dks izHkkfor djus okys dkjd
Concentration of reactant
Surface area of reactants
Nature of reactants
Temperature
Effect of Radiation
Catalyst
Class - XII Topic : Chemical Kinetics
 Factors affecting rate of reaction
izfrfØ;k dh nj dks izHkkfor djus okys dkjd
Concentration of reactant
Rate of reaction α concentration of reactant

Class - XII Topic : Chemical Kinetics

 The rate of a chemical reaction is directly
proportional to the concentration of reactants.
fdlh izfrfØ;k dh nj mlds izfrdkjd ds lkUnzrk dk
lh/kk lekuqikrh gksrk gSA
Higher the concentration of reactant, more and
more reactants collide with each other and
reactants convert into product.
fdlh izfrdkjd dh lkUnzrk vf/kd gksus ij mlds
izfrdkjd ds v.kqvksa esa VDdj dh la[;k vf/kd gksus ij
izfrQy esa ifjoÙkZu vf/kd gksrk gSA

Class - XII Topic : Chemical Kinetics

 Number of effective collisions increase with
increase in temperature.
rki esa o`f) gksus ij izHkkodkjh VDdj dh la[;k vf/kd
gksrh gSA
Hence the rate of reaction increases by
increase in concentration of reactant.
fdlh izfrfØ;k esa izfrdkjd dh lkUnzrk esa o`f) djus ij
mlds nj esa Hkh o`f) gksrh gSA

Class - XII Topic : Chemical Kinetics

 Surface area of reactants
lrgh {ks=Qy dk izfrdkjd
Rate of reaction α surface area

The rate of a chemical reaction increases with

increase in surface area of reactants.
fdlh izfrfØ;k dh nj mlds izfrdkjd ds lrgh {ks=Qy esa
o`f) gksus ij c<+rh gSA

Class - XII Topic : Chemical Kinetics

 Larger surface area has greater contact of
reactants which increases the rate of a
chemical reaction.
lrgh {ks=Qy T;knk gksus ij izfrdkjdksa dk vkil esa
laidZ T;knk gksrk gSA

Rate of reaction Surface area of reactant

Class - XII Topic : Chemical Kinetics

 Nature of reactants
izd`fr dk izfrdkjd
Rate of reaction α Ionic nature of reactant

1
Rate of reaction =
No. of bonds involve

Class - XII Topic : Chemical Kinetics

 The rate of a chemical reaction depends on
ionic character of reactants.
fdlh izfrfØ;k dh nj mlds izfrdkjd ds vk;fud xq.k
ij fuHkZj djrk gSA
Higher the ionic character, greater the rate of
reaction.
izfrdkjd esa vk;fud xq.k ftruk gh vf/kd gksrk gS
mlds izfrfØ;k dh nj mruh gh rhoz gksrh gSA
A chemical reaction has higher rate when
there is participation of less number of bonds.
og izfrfØ;k ftlesa izfrdkjd ds de la[;k esa ca/ku dh
Hkkxsnkjh gksrh gS] mldh nj rhoz gksrh gSA
Class - XII Topic : Chemical Kinetics
 Temperature ¼rki½

Rate of reaction  temperature

The rate of a chemical reaction increases with

increase in temperature.
fdlh izfrfØ;k dh nj mlds rki esa o`f) djus ij c<+rh gSA

Class - XII Topic : Chemical Kinetics

 Increase in temperature increases the
number of effective collisions.
rki esa o`f) djus ij vljnkj VDdjksa dh la[;k c<+rh
gSA
Hence rate of reaction also increases with
increase in temperature.
vr% rki esa o`f) djus ij izfrfØ;k dh nj c<+rh gSA

Class - XII Topic : Chemical Kinetics

 It becomes doubled by increase in
temperature about 10oC.
fdlh izfrfØ;k dh nj nks xq.kh gks tkrh gS] ;fn rki esa
10oC dh o`f) gksA
The rate of a chemical reaction at 20oC = r
The rate of a chemical reaction at 30oC = 2r

The rate of a chemical reaction at 40oC = 4r

Class - XII Topic : Chemical Kinetics

 Effect of Radiation ¼fodj.k½

Rate of reaction α Photons (Packet of light energy)

Rate of reaction α Intensity of absorbed

radiation.

The rate of a photo chemical reaction

increases in presence of suitable radiation.
og jklk;fud izfrfØ;k ftldh fuHkZjrk fodj.k ij gksrh
gS ml izfrfØ;k dh nj mi;qDr fodj.k dh mifLFkfr esa
vf/kd gksrh gSA
Class - XII Topic : Chemical Kinetics
 Catalyst ¼mRizsjd½
The rate of a chemical reaction increases in
presence of positive catalyst.
fdlh izfrfØ;k dh nj /kukRed mRizsjd dh mifLFkfr esa
c<+rh gSA
Positive catalyst decreases the energy
barrier of reactants.
/kukRed mRizsjd dh mifLFkfr esa izfrdkjd dh energy
barrier dk eku de gksrk gSA

Class - XII Topic : Chemical Kinetics

 Hence large number of reactants are
converted into products.
vr% dkQh la[;k esa izfrdkjd dk ifjoÙkZu izfrQy esa
gksrk gSA

Class - XII Topic : Chemical Kinetics

 Law of Mass
Action
nzO;eku lfØ;rk
dk fu;e
Class - XII Topic : Chemical Kinetics
 Law of Mass Action

nzO;eku lfØ;rk dk fu;e

Reaction having one reactant
The rate of a chemical reaction is directly
proportional to the molar concentration (Partial
pressure) or active mass of reactant.
fdlh izfrfØ;k dh nj mlds izfrdkjd ds eksyj
lkUnzrk ;k vkaf'kd nkc dk lh/kk lekuqikrh gksrk gSA

Class - XII Topic : Chemical Kinetics

 Law of Mass Action
nzO;eku lfØ;rk dk fu;e
At constant temperature. Experiment
fu;r rki ij
R P
R =100

P 0

Class - XII Topic : Chemical Kinetics

 Example - 1

R P

r [R]

Class - XII Topic : Chemical Kinetics

 Reaction having Two reactants
izfrfØ;k esa nks izfrdkjdksa dh mifLFkfr
The rate of a chemical reaction is directly
proportional to the product of molar
concentration or partial pressure of reactants.
fdlh izfrfØ;k dh nj mlds izfrdkjd ds eksyj lkUnzrk
;k vkaf'kd nkc ds xq.kuQy dk lh/kk lekuqikrh gksrk gSA

Class - XII Topic : Chemical Kinetics

 Example-2

A+ B AB

r [A] . [B]

Class - XII Topic : Chemical Kinetics

 Example - 3
2A + 3B A2 B3
A +A + B + B + B A2B3

r [A] [A]. [B] [B] [B]

r [A] 2 . [B] 3

Class - XII Topic : Chemical Kinetics

 Law of mass action

Example - 4

aA + bB cC + dD

r [A]a . [B]b

Class - XII Topic : Chemical Kinetics

 Reaction having more than Two reactants
izfrfØ;k esa nks ls vf/kd izfrdkjdksa dh mifLFkfr
The rate of a chemical reaction is directly proportional to the
product of molar concentration or partial pressure of
reactants.
fdlh izfrfØ;k dh nj mlds izfrdkjd ds eksyj lkUnzrk ;k vkaf'kd
nkc ds xq.kuQy dk lh/kk lekuqikrh gksrk gSA
The coefficient of the reactants raised to the power of
molar concentrations or partial pressure .
izfrdkjd dk xq.kd mlds eksyj lkUnzrk ;k vkaf'kd nkc ds ?kkr ij
pyk tkrk gSA
Class - XII Topic : Chemical Kinetics
 Law of Mass action
The rate of a chemical reaction is directly
proportional to the product of molar
concentration or partial pressure of reactants and
coefficient raised to the power.
fdlh izfrfØ;k dh nj mlds izfrdkjd ds eksyj lkUnzrk ;k
vkaf'kd nkc ds xq.kuQy dk lh/kk lekuqikrh gksrk gSA
mldk xq.kd ?kkr ij pyk tkrk gSA
a.A + b.B c.C + d.D

Class - XII Topic : Chemical Kinetics

 The coefficient raised to the power of molar
concentration of reactants.
izfrdkjd dk xq.kd eksyj lkUnzrk ds ?kkr ij pyk tkrk
gSA
a.A+b.B c . C + d. D
r α [A]a [B]b

r α PAa . PBb

Class - XII Topic : Chemical Kinetics

 It is a theoretical fact.
;g ,d lS)kafrd eku gSA
It may or may not be actual observed value
of rate of reaction.
bldk eku izk;ksfxd izfrfØ;k dh nj ds eku ds leku
;k vleku gks ldrk gSA

Class - XII Topic : Chemical Kinetics

 It depends on stoichiometric coefficient.
;g izfrdkjd ds xq.kd ij fuHkZj djrk gSA
Law of mass action may or may not equal to
rate law derivation.
nzO;eku lfØ;rk dk O;atd dk eku izfrfØ;k dh nj ds
O;atd ds leku ;k vleku gks ldrk gSA

Class - XII Topic : Chemical Kinetics

 Rate law derivation Or Rate expression

izfrfØ;k ds nj dk O;atd
At a give temperature, the rate of a reaction
depend on concentration of one or more
reactions.
fdlh izfrfØ;k dh nj fn;s x;s rki ij mlds ,d ;k ,d
ls vf/kd izfrdkjd dh lkanzrk ij fuHkZj djrk gSA

Class - XII Topic : Chemical Kinetics

 The rate law derivation of a chemical
reaction does not depend on stoichiometric
coefficient.
fdlh jklk;fud izfrfØ;k ds nj dk O;atd mldss
izfrdkjd ds xq.kd ij fuHkZj ugha djrk gSA
The power on concentration of reaction may
or may not be equal to stoichiometric
coefficient.
izfrfØ;k ds nj ds O;atd esa mifLFkr izfrdkjd ds
lkanzrk dk ?kkr ml izfrdkjd ds xq.kd ds leku gks Hkh
ldrk gS ;k ugha gks ldrk gSA
Class - XII Topic : Chemical Kinetics
 a.A b.B

Law of mass action r [A]a

Rate law derivation r [A]x

x is determined experimentally.

Class - XII Topic : Chemical Kinetics

 a.A+b.B c . C + d. D

Law of mass action r [A]a [B]b

r k [A]a [B]b

Rate law derivation r k [A]x [B]y

x, y, determined experimentally.

Class - XII Topic : Chemical Kinetics

 It is experimental fact.
;g ,d izk;ksfxd eku gSA
Rate law gives the actual observed rate.
;g izfrfØ;k ds nj dh lgh O;k[;k djrk gSA
It has no relation with stoichiometry
coefficient.
blds eku dk izfrdkjd ds xq.kd ls dksbZ laca/k ugha
gksrk gSA

Class - XII Topic : Chemical Kinetics

 Rate of reaction at different concentration
can be determined with the help of rate law.
bl O;atd }kjk izfrfØ;k ds nj dk fu/kkZj.k fofHkUu
lkUnzrk ij fd;k tkrk gSA

Class - XII Topic : Chemical Kinetics

 Rate Constant ¼nj fLFkjkad½

Rate of a reaction.
izfrfØ;k dh njA
When reactants have unit molar concentration
;fn izfrdkjd dh lkUnzrk bdkbZ gksA
It is called rate constant.
bls osx fLFkjkad dgrs gSaA

Class - XII Topic : Chemical Kinetics

 Let a reaction is a nth order reaction.
ekuk fd ,d izfrfØ;k nth dksfV dh izfrfØ;k gSA

A B
Rate of reaction, r [A]n
r K [A]n

r
K = Let, [A] = 1
[A]n

Class - XII Topic : Chemical Kinetics

 Rate Constant or Velocity Constant

osx fLFkjkad
Rate constant of a reaction is the rate of reaction
when concentration of all the reactants are unit.
fdlh izfrfØ;k esa ;fn mifLFkr izfrdkjd dh lkUnzrk bdkbZ
gks rks ml izfrfØ;k dh nj gh osx fLFkjkad dgykrh gSA

Class - XII Topic : Chemical Kinetics

 Rate Constant ¼nj fLFkjkad½
A B
Rate of reaction, r K [A]n

K = Rate constant ¼nj fLFkjkad½

Or , K= Velocity constant ¼osx fLFkjkad½

Or , K= Specific rate constant

¼fof'k"V nj fLFkjkad½
Class - XII Topic : Chemical Kinetics
 Unit of Rate Constant
A B
r
K =
[A]n

K = ( litre)n-1mole 1 – n sec-1
K = ( atm) 1-n sec-1

Class - XII Topic : Chemical Kinetics

 Unit of rate constant

osx fLFkjkad dk ek=d

Let a reaction is a nth order reaction.
ekuk fd ,d izfrfØ;k n dksfV dh izfrfØ;k gSA
A B
r [A]n

r K [A]n

Class - XII Topic : Chemical Kinetics

 Points

It is denoted by K
bldk ladsr K gksrk gSA
Rate constant has definite value at a
particular temperature
osx fLFkjkad dk eku fu;r rki ij fuf'pr gksrk gSA

Class - XII Topic : Chemical Kinetics

 The value of rate constant does not depends
on concentration of reactant.
osx fLFkjkad dk eku izfrdkjd dh lkUnzrk ij fuHkZj ugha
djrk gSA
The unit of rate constant depends on order of
reaction.
osx fLFkjkad dk eku fdlh izfrfØ;k ds dksfV ij fuHkZj
djrk gSA
K = ( litre)n-1mole 1 – n sec-1
K = ( atm) 1-n sec-1

Class - XII Topic : Chemical Kinetics

 The value of rate constant changes with
change in temperature.
osx fLFkjkad dk eku rki esa ifjoÙkZu djus ij ifjofÙkZr
gksrk gSA
The value of rate constant does not depends
on concentration of reactant.
osx fLFkjkad dk eku izfrdkjd dh lkUnzrk ij fuHkZj
ugha djrk gSA
The unit of rate constant depends on order of
reaction.
osx fLFkjkad dk eku fdlh izfrfØ;k ds dksfV ij fuHkZj
djrk gSA
Class - XII Topic : Chemical Kinetics
 Order of Reaction
izfrfØ;k dh nj
For a reaction
fdlh izfrfØ;k dsA
Rate law derivation (Rate expression)
nj ds O;atd esa A
Reactants
izfrdkjd dh
Molar concentration power or exponent
eksyj lkUnzrk ds ?kkr

Class - XII Topic : Chemical Kinetics

 Number – experimentally determined.
la[;k ftldk fu/kkZj.k izk;ksfxd gksrk gSA
Number – sum – order of reaction.
ml la[;k ds ;ksx dks izfrfØ;k dh dksfV dgrs gSaA

Class - XII Topic : Chemical Kinetics

 Order of Reaction ¼izfrfØ;k dh nj½
The sum of power of molar concentration or
pressure of reacting species in rate law derivation
is called order of reaction.
fdlh izfrfØ;k dh nj ds O;atd esa mifLFkr izfrdkjd ds
eksyj lkUnzrk ;k vkaf'kd nkc ds ?kkrksa ds ;ksx dks ml
izfrfØ;k dh dksfV dgrs gSaA

Class - XII Topic : Chemical Kinetics

 A+B C+D

Rate of reaction = K [A]x [B]y

X,Y are determined experimentally.

X, Y dk fu/kkZj.k iz;ksx }kjk gksrk gSA

Class - XII Topic : Chemical Kinetics

 Order of reaction w.r.t A = X
A ds lkis{k izfrfØ;k dh dksfV = X

Order of reaction w.r.t B = Y

B ds lkis{k izfrfØ;k dh dksfV = Y

Total order of reaction = X + Y

izfrfØ;k dh dqy dksfV = X + Y

Class - XII Topic : Chemical Kinetics

 Points
It is an experimental quantity.
;g ,d izk;ksfxd in gSA
It may be negative , zero, positive and
fractional,.
;g _.kkRed] 'kqU;] /kukRed] fHkUu gks ldrk gSA
Order of reaction cannot be predicted by
observing the coefficient of reactants.
fdlh izfrfØ;k ds dksfV dk fu/kkZj.k mlds izfrdkjd ds
xq.kd dks ns[kdj ugha fd;k tk ldrk gSA
Class - XII Topic : Chemical Kinetics
 The order of reaction may or may not be
equal to the sum of stoichiometry coefficient
fdlh izfrfØ;k ds dksfV mlds izfrdkjd ds xq.kd ds
leku ;k leku ugha gks ldrk gSA
It does not depend on mechanism of a
reaction.
;g izfrfØ;k ds fØ;kfof/k ij fuHkZj ugha djrk gSA
Order of reaction change with change in
temperature and concentration.
fdlh izfrfØ;k dh dksfV mlds rki rFkk lkUnzrk esa
ifjoÙkZu djus ij ifjofÙkZr gks tkrh gSA
Class - XII Topic : Chemical Kinetics
SANKALP EDUCATION
CLASS- 12
Physical chemistry
Unit – CHEMICAL KINETICS
Pat – 1 completed
Class - XII Topic : Chemical Kinetics