XI_EQUILIBRIUM_ Class Xi by cbse 11 .ppt

EQUILIBRIUM IN PHYSICAL PROCESSES
EQUILIBRIUM IN PHYSICAL PROCESSES
3
• Liquid-Vapour Equilibrium
Liquid-Vapour Equilibrium
• Evaporation.
Evaporation.
• Condensation.
Condensation.
• Solid-Liquid Equilibrium
Solid-Liquid Equilibrium
• Freezing.
Freezing.
• Melting (Fusion).
Melting (Fusion).
• Solid – Vapour Equilibrium
Solid – Vapour Equilibrium
• Sublimation.
Sublimation.
Define boiling point.
Why food get cooked fast and
easily in a pressure cooker???

EQUILIBRIUM INVOLVING DISSOLUTION
EQUILIBRIUM INVOLVING DISSOLUTION
OF SOLID OR GASES IN LIQUIDS
OF SOLID OR GASES IN LIQUIDS
• Gases in liquids.
Gases in liquids.
• Aerated drinks like cold drinks,
Aerated drinks like cold drinks,
beer and champagne.
beer and champagne.
• Solids in liquids
Solids in liquids
• Saturated and super saturated
Saturated and super saturated
solutions.
solutions.
4

EQUILIBRIUM IN CHEMICAL PROCESSES –
EQUILIBRIUM IN CHEMICAL PROCESSES –
DYNAMIC EQUILIBRIUM
DYNAMIC EQUILIBRIUM
• For a chemical reaction, if the rate of
For a chemical reaction, if the rate of
forward reaction is equal to backward
forward reaction is equal to backward
reaction then,
reaction then,
• There is no net change in the
There is no net change in the
concentration of eather reactant or
concentration of eather reactant or
product.
product.
• This is known as the state of equilibria.
This is known as the state of equilibria.
• Equilibria is the singular form of
Equilibria is the singular form of
equilibrium.
equilibrium.
• A + B
A + B ⇌
⇌ C + D
C + D
5

LAW OF MASS ACTION
LAW OF MASS ACTION
6

LAW OF CHEMICAL EQUILIBRIUM
LAW OF CHEMICAL EQUILIBRIUM
AND EQUILIBRIUM CONSTANT
AND EQUILIBRIUM CONSTANT
• It states that when a Chemical reaction is in
It states that when a Chemical reaction is in
equilibrium, at a particular set of
equilibrium, at a particular set of
thermodynamic condition ( Constant P, V, n, T),
thermodynamic condition ( Constant P, V, n, T),
• the
the RATIO OF CONCENTRATION
RATIO OF CONCENTRATION of product
of product
to the concentration of reactant, raised power
to the concentration of reactant, raised power
their
their STOICHIOMETRIC COEFFICIENT
STOICHIOMETRIC COEFFICIENT, will
, will
always be
always be CONSTANT
CONSTANT.
.
• This constant is denoted by
This constant is denoted by K
KC
C and is known as
and is known as
EQUILIBRIUM CONSTANT
EQUILIBRIUM CONSTANT.
.
• In the expression of K
In the expression of KC
C, the
, the concentration of
concentration of
Solid and Liquid reactant or product is taken
Solid and Liquid reactant or product is taken
as one.
as one.
7

HOMOGENEOUS & HETEROGENEOUS EQUILIBRIA
HOMOGENEOUS & HETEROGENEOUS EQUILIBRIA
• In a homogeneous system, all the reactants and
In a homogeneous system, all the reactants and
products are in the same phase or physical state.
products are in the same phase or physical state.
• N
N2
2(g) + 3H
(g) + 3H2
2(g) 2NH
⇌
(g) 2NH
⇌ 3
3(g),
(g),
• CH
CH3
3COOC
COOC2
2H
H5
5 (aq) + H
(aq) + H2
2O (l) CH
⇌
O (l) CH
⇌ 3
3COOH (aq) + C
COOH (aq) + C2
2H
H5
5OH (aq)
OH (aq)
• Fe
Fe3+
3+
(aq) + SCN
(aq) + SCN ––
––
(aq) Fe(SCN)
⇌
(aq) Fe(SCN)
⇌ 2+
2+
(aq)
(aq)
• Equilibrium in a system having more than one phase
Equilibrium in a system having more than one phase
is called heterogeneous equilibrium.
is called heterogeneous equilibrium.
• Ca(OH)
Ca(OH)2
2 (s) + (aq) Ca
⇌
(s) + (aq) Ca
⇌ 2+
2+
(aq) + 2OH
(aq) + 2OH–
–
(aq)
(aq)
• CaCO
CaCO3
3 (s)
(s) ⇌
⇌ CaO (s) + CO
CaO (s) + CO2
2 (g)
(g)
• In the expression of K
In the expression of KC
C, the
, the concentration of Solid and Liquid reactant or
concentration of Solid and Liquid reactant or
product is taken as one.
product is taken as one.
9

APPLICATIONS OF EQUILIBRIUM CONSTANTS
APPLICATIONS OF EQUILIBRIUM CONSTANTS
• Predict the extent of a reaction on the basis of its
Predict the extent of a reaction on the basis of its
magnitude,
magnitude,
• Predict the direction of the reaction, and
Predict the direction of the reaction, and
• Calculate equilibrium concentrations.
Calculate equilibrium concentrations.
10

PREDICTING THE EXTENT OF A REACTION
PREDICTING THE EXTENT OF A REACTION
• If
If Kc > 10
Kc > 103
3
,
, products predominate
products predominate over reactants, i.e.,
over reactants, i.e.,
if Kc is very large, the reaction proceeds
if Kc is very large, the reaction proceeds nearly to
nearly to
completion
completion.
.
• If
If Kc < 10
Kc < 10–3
–3
,
, reactants predominate
reactants predominate over products, i.e.,
over products, i.e.,
if Kc is very small, the
if Kc is very small, the reaction proceeds rarely
reaction proceeds rarely.
.
• If Kc is in the
If Kc is in the range of 10
range of 10–3
–3
to 10
to 103
3
, appreciable
, appreciable
concentrations of both reactants and products are
concentrations of both reactants and products are
present.
present.
11

PREDICT THE DIRECTION OF THE REACTION
PREDICT THE DIRECTION OF THE REACTION
12

A MIXTURE OF 1.57 MOL OF N
A MIXTURE OF 1.57 MOL OF N2
2, 1.92 MOL OF H
, 1.92 MOL OF H2
2 AND 8.13 MOL OF NH
AND 8.13 MOL OF NH3
3 IS INTRODUCED INTO A
IS INTRODUCED INTO A
20 L REACTION VESSEL AT 500 K. AT THIS TEMPERATURE, THE EQUILIBRIUM CONSTANT, K
20 L REACTION VESSEL AT 500 K. AT THIS TEMPERATURE, THE EQUILIBRIUM CONSTANT, KC
C
FOR THE REACTION N
FOR THE REACTION N2
2 (G) + 3H
(G) + 3H2
2 (G) 2NH
⇌
(G) 2NH
⇌ 3
3 (G) IS 1.7 × 10
(G) IS 1.7 × 102
2
. IS THE REACTION MIXTURE AT
. IS THE REACTION MIXTURE AT
EQUILIBRIUM? IF NOT, WHAT IS THE DIRECTION OF THE NET REACTION?
EQUILIBRIUM? IF NOT, WHAT IS THE DIRECTION OF THE NET REACTION?
13

CALCULATING EQUILIBRIUM CONCENTRATIONS
CALCULATING EQUILIBRIUM CONCENTRATIONS
14

WHAT IS THE EQUILIBRIUM CONCENTRATION OF EACH OF THE SUBSTANCES IN THE
WHAT IS THE EQUILIBRIUM CONCENTRATION OF EACH OF THE SUBSTANCES IN THE
EQUILIBRIUM WHEN THE INITIAL CONCENTRATION OF ICl WAS 0.78 M ?
EQUILIBRIUM WHEN THE INITIAL CONCENTRATION OF ICl WAS 0.78 M ?
2ICl (G) I
⇌
2ICl (G) I
⇌ 2
2 (G) + Cl
(G) + Cl2
2 (G); K
(G); KC
C = 0.14
= 0.14
29/01/25 15
ICl I2 Cl
2
Initial 0.78 M 0 0
At
equilibriu
m
0.78 –
2X
X X

RELATION BETWEEN K
RELATION BETWEEN KC
C AND K
AND KP
P
16

FOR THE EQUILIBRIUM, 2NOCL(G) 2NO(G) + CL
⇌
FOR THE EQUILIBRIUM, 2NOCL(G) 2NO(G) + CL
⇌ 2
2(G) THE VALUE OF THE
(G) THE VALUE OF THE
EQUILIBRIUM CONSTANT, K
EQUILIBRIUM CONSTANT, KC
C IS 3.75 × 10
IS 3.75 × 10–6
–6
AT 1069 K. CALCULATE THE
AT 1069 K. CALCULATE THE
K
KP
P FOR THE REACTION AT THIS TEMPERATURE?
FOR THE REACTION AT THIS TEMPERATURE?
•We know that,
We know that,
•K
Kp
p = K
= Kc
c(RT)
(RT)Δ
Δn
n
•For the above reaction,
For the above reaction,
•Δ
Δn = (2+1) – 2 = 1
n = (2+1) – 2 = 1
•Kp = 3.75 ×10
Kp = 3.75 ×10–6
–6
(0.0831 × 1069)
(0.0831 × 1069)
•Kp = 0.033
Kp = 0.033
17

PHOSPHORUS PENTACHLORIDE GAS PARTIALLY DECOMPOSES TO PHOSPHORUS
PHOSPHORUS PENTACHLORIDE GAS PARTIALLY DECOMPOSES TO PHOSPHORUS
TRICHLORIDE GAS AND CHLORINE GAS. 1.20 MOL PCL5 IS PLACED IN A 1.00 L CONTAINER
TRICHLORIDE GAS AND CHLORINE GAS. 1.20 MOL PCL5 IS PLACED IN A 1.00 L CONTAINER
AT 200 °C. AT EQUILIBRIUM 1.00 MOL PCL
AT 200 °C. AT EQUILIBRIUM 1.00 MOL PCL5
5 REMAINS. CALCULATE K
REMAINS. CALCULATE KC
C AND K
AND KP
P AT 200 °C.
AT 200 °C.
18
PCl5 PCl3 Cl2
Initial 1.2 0 0
At equilibrium 1.0 0.2 0.2

RELATIONSHIP BETWEEN EQUILIBRIUM CONSTANT
RELATIONSHIP BETWEEN EQUILIBRIUM CONSTANT
K, REACTION QUOTIENT Q AND GIBBS ENERGY G
K, REACTION QUOTIENT Q AND GIBBS ENERGY G
• Δ
ΔG =
G = Δ
ΔG
G0
0
+ RT lnQ
+ RT lnQ
• Where, G
Where, G0
0
is standard Gibbs energy.
is standard Gibbs energy.
• At equilibrium,
At equilibrium,
• Δ
ΔG = 0 and Q = Kc
G = 0 and Q = Kc,
,
• The above equation becomes,
The above equation becomes,
• 0
0 =
= Δ
ΔG
G0
0
+ RT ln Kc
+ RT ln Kc
• Δ
ΔG
G0
0
= – RT ln Kc
= – RT ln Kc
• Δ
ΔG
G0
0
= – 2.303 RT log Kc
= – 2.303 RT log Kc
19

HYDROLYSIS OF SUCROSE GIVES, SUCROSE + H
HYDROLYSIS OF SUCROSE GIVES, SUCROSE + H2
2O
O ⇌
⇌
GLUCOSE + FRUCTOSE
GLUCOSE + FRUCTOSE EQUILIBRIUM CONSTANT
EQUILIBRIUM CONSTANT K
KC
C FOR THE
FOR THE
REACTION IS 2 ×10
REACTION IS 2 ×1013
13
AT 300K. CALCULATE
AT 300K. CALCULATE 
G
G0
0
AT
AT 300K.
300K.
20

THE VALUE OF
THE VALUE OF 
G
G0
0
FOR THE PHOSPHORYLATION
FOR THE PHOSPHORYLATION OF
OF
GLUCOSE IN GLYCOLYSIS IS 13.8 KJ/MOL.
GLUCOSE IN GLYCOLYSIS IS 13.8 KJ/MOL. FIND THE
FIND THE
VALUE OF
VALUE OF K
KC
C AT 298 K.
AT 298 K.
21

FACTORS AFFECTING EQUILIBRIA
FACTORS AFFECTING EQUILIBRIA
LE CHATELIER’S PRINCIPLE
LE CHATELIER’S PRINCIPLE
• If the state of
If the state of equilibria is disturbed
equilibria is disturbed by changing
by changing
temperature, pressure, volume or the amount of
temperature, pressure, volume or the amount of
reactant or product then,
reactant or product then,
• The
The reaction adjust itself in such a way that the
reaction adjust itself in such a way that the
effect of that change is minimized and thus try to
effect of that change is minimized and thus try to
attain equilibrium again
attain equilibrium again.
.
• This is applicable to all physical and chemical
This is applicable to all physical and chemical
equilibria.
equilibria.
22

EFFECT OF CONCENTRATION CHANGE
EFFECT OF CONCENTRATION CHANGE
• We already had discussed this topic.
We already had discussed this topic.
• Any guesses ????
Any guesses ????
• At equilibrium, if the
At equilibrium, if the CONCENTRATION OF REACTANT IS
CONCENTRATION OF REACTANT IS
INCREASED
INCREASED, then the reaction is favored in
, then the reaction is favored in FORWARD DIRECTION
FORWARD DIRECTION.
.
At equilibrium, if the CONCENTRATION OF REACTANT IS
CONCENTRATION OF REACTANT IS
DECREASED
DECREASED, then the reaction is favored in
, then the reaction is favored in BACKWARD DIRECTION
BACKWARD DIRECTION.
.
At equilibrium, if the CONCENTRATION OF PRODUCT IS DECREASED
CONCENTRATION OF PRODUCT IS DECREASED,
,
then the reaction is favored in
then the reaction is favored in FORWARD DIRECTION
FORWARD DIRECTION.
.
At equilibrium, if the CONCENTRATION OF PRODUCT IS INCREASED
CONCENTRATION OF PRODUCT IS INCREASED,
,
then the reaction is favored in
then the reaction is favored in BACKWARD DIRECTION
BACKWARD DIRECTION.
.
• Jump to Slide no 14 for detailed explanation.
Jump to Slide no 14 for detailed explanation.
23

EFFECT OF PRESSURE CHANGE
EFFECT OF PRESSURE CHANGE
24

EFFECT OF TEMPERATURE CHANGE
•In general, the temperature dependence of the equilibrium constant
In general, the temperature dependence of the equilibrium constant
depends on the sign of
depends on the sign of Δ
ΔH for the reaction.
H for the reaction.
•∆
∆G = ∆H – T ∆S
G = ∆H – T ∆S
•∆
∆G
G0
0
= – 2.303 RT LOG (K
= – 2.303 RT LOG (KC
C)
)
• The equilibrium constant for an exothermic reaction (negative
The equilibrium constant for an exothermic reaction (negative Δ
ΔH)
H)
decreases as the temperature increases.
decreases as the temperature increases.
• Hence backward reaction is favored with the increase in temperature.
Hence backward reaction is favored with the increase in temperature.
• The equilibrium constant for an endothermic reaction (positive
The equilibrium constant for an endothermic reaction (positive Δ
ΔH)
H)
increases as the temperature increases.
increases as the temperature increases.
• Hence forward reaction is favored with the increase in temperature.
Hence forward reaction is favored with the increase in temperature.
• Temperature changes affect the equilibrium constant and rates of
Temperature changes affect the equilibrium constant and rates of
reactions.
reactions. 25

26

EFFECT OF INERT GAS ADDITION
EFFECT OF INERT GAS ADDITION
• If the
If the volume is kept constant
volume is kept constant and an inert gas such as
and an inert gas such as
argon is added which
argon is added which does not take part in the reaction
does not take part in the reaction,
,
• Then
Then THE EQUILIBRIUM REMAINS UNDISTURBED.
THE EQUILIBRIUM REMAINS UNDISTURBED.
• It is because the addition of an inert gas at constant volume
It is because the addition of an inert gas at constant volume
does not change the
does not change the PARTIAL PRESSURES
PARTIAL PRESSURES or the
or the MOLAR
MOLAR
CONCENTRATIONS
CONCENTRATIONS of the substance involved in the
of the substance involved in the
reaction.
reaction.
• The reaction quotient changes only if the added gas is a
The reaction quotient changes only if the added gas is a
reactant or product involved in the reaction.
reactant or product involved in the reaction.
27

EFFECT OF A CATALYST
EFFECT OF A CATALYST
• In the state of equilibria,
In the state of equilibria, ADDITION OF CATALYST WILL
ADDITION OF CATALYST WILL
HAVE NO EFFECT
HAVE NO EFFECT.
.
• The catalyst will only help in
The catalyst will only help in attending equilibrium faster
attending equilibrium faster but
but
will have on effect on the state of equilibria.
will have on effect on the state of equilibria.
• This is because,
This is because, a catalyst increases the rate of forward and
a catalyst increases the rate of forward and
reverse reactions (
reverse reactions (EQUALLY
EQUALLY)
) that pass through the same
that pass through the same
transition state and does not affect equilibrium.
transition state and does not affect equilibrium.
• In other words,
In other words, Catalyst lowers the activation energy
Catalyst lowers the activation energy for the
for the
forward and reverse reactions by exactly the same amount.
forward and reverse reactions by exactly the same amount.
• If a reaction has an exceedingly small K
If a reaction has an exceedingly small KC
C, a catalyst would be of
, a catalyst would be of
little help
little help.
.
28

WHICH OF THE FOLLOWING REACTIONS WILL GET
WHICH OF THE FOLLOWING REACTIONS WILL GET AFFECTED BY INCREASING THE
AFFECTED BY INCREASING THE
PRESSURE
PRESSURE? ALSO, MENTION WHETHER CHANGE WILL CAUSE THE REACTION TO GO
? ALSO, MENTION WHETHER CHANGE WILL CAUSE THE REACTION TO GO
INTO FORWARD OR BACKWARD DIRECTION.
INTO FORWARD OR BACKWARD DIRECTION.
• COCl
COCl2
2 (g) CO (g) + Cl
⇌
(g) CO (g) + Cl
⇌ 2
2 (g)
(g)
• CH
CH4
4 (g) + 2S
(g) + 2S2
2 (g) CS
⇌
(g) CS
⇌ 2
2 (g) + 2H
(g) + 2H2
2S (g)
S (g)
• CO
CO2
2 (g) + C (s) 2CO (g)
⇌
(g) + C (s) 2CO (g)
⇌
• 2H
2H2
2 (g) + CO (g) CH
⇌
(g) + CO (g) CH
⇌ 3
3OH (g)
OH (g)
• CaCO
CaCO3
3 (s) CaO (s) + CO
⇌
(s) CaO (s) + CO
⇌ 2
2 (g)
(g)
• 4 NH
4 NH3
3 (g) + 5O
(g) + 5O2
2 (g) 4NO (g) + 6H
⇌
(g) 4NO (g) + 6H
⇌ 2
2O(g)
O(g)
29
BACKWARD DIRECTION.
NO CHANGE
BACKWARD DIRECTION.
FORWARD DIRECTION.
BACKWARD DIRECTION.
BACKWARD
DIRECTION.

HOW THE EQUILIBRIUM OF THE REACTION:
HOW THE EQUILIBRIUM OF THE REACTION:
2H
2H2
2(G) + CO (G) CH
⇌
(G) + CO (G) CH
⇌ 3
3OH (G) ;
OH (G) ;
WILL BE AFFECTED ON
WILL BE AFFECTED ON
a)
a) addition of H
addition of H2
2
FORWARD DIRECTION
FORWARD DIRECTION
b) addition of CH
b) addition of CH3
3OH
OH
BACKWARD DIRECTION
BACKWARD DIRECTION
30
c) removal of CO
BACKWARD DIRECTION
d) removal of CH3OH
FORWARD DIRECTION

ACIDS, BASES AND SALTS
ACIDS, BASES AND SALTS
31

ARRHENIUS CONCEPT OF ACIDS AND BASES
ARRHENIUS CONCEPT OF ACIDS AND BASES
32

LEWIS CONCEPT OF ACIDS AND BASES
LEWIS CONCEPT OF ACIDS AND BASES
•G.N. Lewis in 1923 defined
G.N. Lewis in 1923 defined
•An acid as a species which
An acid as a species which ACCEPTS
ACCEPTS
ELECTRON PAIR
ELECTRON PAIR and
and
•Base as a species which
Base as a species which DONATES AN
DONATES AN
ELECTRON PAIR
ELECTRON PAIR.
.
•BF
BF3
3 + : NH
+ : NH3
3 BF
→ BF
→ 3
3:NH
:NH3
3
33
LEWIS ACID LEWIS BASE

THE BRÖNSTED-LOWRY ACIDS AND BASES
THE BRÖNSTED-LOWRY ACIDS AND BASES
• This concept of ACID & BASE was
This concept of ACID & BASE was
given by Danish chemist,
given by Danish chemist,
Johannes Brönsted
Johannes Brönsted and the
and the
English chemist,
English chemist, Thomas M.
Thomas M.
Lowry
Lowry.
.
• THE SUBSTANCE THAT
THE SUBSTANCE THAT GIVE H
GIVE H+
+
ION
ION ARE ACID.
ARE ACID.
• THE SUBSTANCE THAT
THE SUBSTANCE THAT ACCEPT
ACCEPT
H
H+
+
ION
ION ARE BASE.
ARE BASE.
• The species formed after the
The species formed after the
donation of acceptation of H
donation of acceptation of H+
+
ION
ION
are known as
are known as CONJUGATES.
CONJUGATES.
34
Water can act both as acid or base.
What such substance called??

29/01/25 35
Species conjugate
acid
conjugate
base
H2O H3O+
OH–
HCO3
–
H2CO3 CO3
2–
HSO4
–
H2SO4 SO4
2–
NH3 NH4
+
NH2
–

THE pH SCALE
THE pH SCALE
36
• The pH scale was invented by the Danish chemist
The pH scale was invented by the Danish chemist
Soren Sorensen to measure the acidity of beer in a
Soren Sorensen to measure the acidity of beer in a
brewery.
brewery. The pH scale measured the
The pH scale measured the
concentration of hydrogen ions in solution
concentration of hydrogen ions in solution. The
. The
more hydrogen ions, the stronger the acid.
more hydrogen ions, the stronger the acid.
• The
The pH
pH of a solution is a measure of how acidic or
of a solution is a measure of how acidic or
basic a solution is.
basic a solution is. A solution that has a pH value
A solution that has a pH value
of exactly 7 is neutral—neither acidic nor basic
of exactly 7 is neutral—neither acidic nor basic.
.
• A solution with
A solution with a pH value of less than 7 is acidic
a pH value of less than 7 is acidic.
.
There are more H
There are more H3
3O
O+
+
ions than OH
ions than OH–
–
ions in the
ions in the
solution.
solution.
• A solution with
A solution with a pH value greater than 7 is basic
a pH value greater than 7 is basic.
.
There are more OH
There are more OH–
–
ions than H
ions than H3
3O
O+
+
ions in the
ions in the
solution.
solution.

HOW IS pH MEASURED?
HOW IS pH MEASURED?
37

BUFFER SOLUTIONS
BUFFER SOLUTIONS
38
• THE SOLUTIONS WHICH RESIST CHANGE IN PH ON
THE SOLUTIONS WHICH RESIST CHANGE IN PH ON
DILUTION OR WITH THE ADDITION OF SMALL AMOUNTS
DILUTION OR WITH THE ADDITION OF SMALL AMOUNTS
OF ACID OR ALKALI
OF ACID OR ALKALI are called Buffer Solutions.
are called Buffer Solutions.
• A mixture of
A mixture of acetic acid and sodium acetate
acetic acid and sodium acetate acts as buffer
acts as buffer
solution around pH 4.75 and
solution around pH 4.75 and
• a mixture of
a mixture of ammonium chloride and ammonium hydroxide
ammonium chloride and ammonium hydroxide
acts as a buffer around pH 9.25.
acts as a buffer around pH 9.25.
• Blood is a natural buffer solution
Blood is a natural buffer solution.
.

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