Chapter 6 -Thermodynamics - Chapter Notes, Chemistry, Class 11 PDF Download

 Page 1


82 
 
CHAPTER 6 
T HE RM ODYN AM I CS” 
Brief Summary of the chapter: 
1. Thermodynamics: Science which deals with study of different forms of 
energy and quantitative relationship. 
2. System & Surroundings: The part of universe for study is called system and 
remaining portion is surroundings. 
3. State of system & state function: State of system is described in terms of T, 
P, V etc. The property which depends only on state of system not upon path 
is called state function eg. P, V, T, E, H, S etc. 
4. Extensive & Intensive Properties: Properties which depends on quantity of 
matter called extensive prop. eg. mass, volume, heat capacity, enthalpy, 
entropy etc. The properties which do not depends on matter present 
depends upon nature of substance called Intensive properties. eg. T,P, 
density, refractive index, viscosity, bp, pH, mole fraction etc. 
5. Internal energy: The total energy with a system. 
i.e. U =  E
e
 + E
n
 + E
c
 + E
p 
+ E
k 
+ ------ 
U = U
2
 – U
1
 or U
P
 – U
R
 & U is state function and extensive properly. If 
U
1
 > U
2
 energy is released. 
6. Heat (q): It I a form of energy which is exchanged between system and 
surrounding due to difference of temperature. Unit is Joule (J) or Calorie (1 
Calorie = 4.18  J). 
7. First Law of Thermodynamics: It is law of conservation energy. Energy can 
neither be created not destroyed, it may be converted from one from into 
another. 
 Mathematically U = q + w, w = –p. V (work of expansion) 
 U = q – p. V or q = U + p. V, q,w are not state function. 
Page 2


82 
 
CHAPTER 6 
T HE RM ODYN AM I CS” 
Brief Summary of the chapter: 
1. Thermodynamics: Science which deals with study of different forms of 
energy and quantitative relationship. 
2. System & Surroundings: The part of universe for study is called system and 
remaining portion is surroundings. 
3. State of system & state function: State of system is described in terms of T, 
P, V etc. The property which depends only on state of system not upon path 
is called state function eg. P, V, T, E, H, S etc. 
4. Extensive & Intensive Properties: Properties which depends on quantity of 
matter called extensive prop. eg. mass, volume, heat capacity, enthalpy, 
entropy etc. The properties which do not depends on matter present 
depends upon nature of substance called Intensive properties. eg. T,P, 
density, refractive index, viscosity, bp, pH, mole fraction etc. 
5. Internal energy: The total energy with a system. 
i.e. U =  E
e
 + E
n
 + E
c
 + E
p 
+ E
k 
+ ------ 
U = U
2
 – U
1
 or U
P
 – U
R
 & U is state function and extensive properly. If 
U
1
 > U
2
 energy is released. 
6. Heat (q): It I a form of energy which is exchanged between system and 
surrounding due to difference of temperature. Unit is Joule (J) or Calorie (1 
Calorie = 4.18  J). 
7. First Law of Thermodynamics: It is law of conservation energy. Energy can 
neither be created not destroyed, it may be converted from one from into 
another. 
 Mathematically U = q + w, w = –p. V (work of expansion) 
 U = q – p. V or q = U + p. V, q,w are not state function. 
83 
 
 But U is state function. 
8. Enthalpy (H): At constant volume V = 0,  q
v
 = U 
 So H = U + p. V, q
p
 = H
2
 H
1
 = H 
 H = U + P. V. 
9. Relationship between q
p
, q
v
 i.e. H& U 
 It is H = U+ ng.RT or q
p
 = q
v + 
 ng.RT 
10. Exothermic and Endothermic reactions: H = –Ve for exothermic and H 
= +Ve for endothermic reaction i.e. evolution and absorption of heat. 
Eg C+O
2
  CO
2
 + 393.5 KJ, H = –393.5 KJ (exothermic) 
N
2
 + O
2
  2NO – 180.7 KJ, H = 180.7 KJ (Endothermic) 
11. Enthalpy of reaction (
r
H): The amount of heat evolved or absorbed when 
the reaction is completed. 
12. Standard Enthalpy of reaction (
r
H
0
) at 1 bar pressure and specific temp. 
(290K) i.e. standard state. 
13. Different types of Enthalpies of reactions: 
(i) Enthalpy of combustion (
c
H),  (ii) Enthalpy of formation (
f
H) 
(iii) Enthalpy of neutralization  (iv) Enthalpy of solution 
(v) Enthalpy of atomization(
a
H), (vi)Enthalpy of Ionisation (
i
H) 
(vii) Enthalpy of Hydration (
hyol.
H) (viii) Enthalpy of fusion (
fus.
H) 
(ix) Enthalpy of vaporization (
vap.
H) (x)Enthalpy of sublimation (
sub.
H) 
 (
sub.
H) = 
fus.
(H) - 
vap
(H) 
14. Hess’s Law of constant heat summation: The total amount of heat change is 
same whether the reaction takes place in one step or in several steps. 
 
i.e. H = H
1
 + H
2
 + H
3 
+ -------- 
Page 3


82 
 
CHAPTER 6 
T HE RM ODYN AM I CS” 
Brief Summary of the chapter: 
1. Thermodynamics: Science which deals with study of different forms of 
energy and quantitative relationship. 
2. System & Surroundings: The part of universe for study is called system and 
remaining portion is surroundings. 
3. State of system & state function: State of system is described in terms of T, 
P, V etc. The property which depends only on state of system not upon path 
is called state function eg. P, V, T, E, H, S etc. 
4. Extensive & Intensive Properties: Properties which depends on quantity of 
matter called extensive prop. eg. mass, volume, heat capacity, enthalpy, 
entropy etc. The properties which do not depends on matter present 
depends upon nature of substance called Intensive properties. eg. T,P, 
density, refractive index, viscosity, bp, pH, mole fraction etc. 
5. Internal energy: The total energy with a system. 
i.e. U =  E
e
 + E
n
 + E
c
 + E
p 
+ E
k 
+ ------ 
U = U
2
 – U
1
 or U
P
 – U
R
 & U is state function and extensive properly. If 
U
1
 > U
2
 energy is released. 
6. Heat (q): It I a form of energy which is exchanged between system and 
surrounding due to difference of temperature. Unit is Joule (J) or Calorie (1 
Calorie = 4.18  J). 
7. First Law of Thermodynamics: It is law of conservation energy. Energy can 
neither be created not destroyed, it may be converted from one from into 
another. 
 Mathematically U = q + w, w = –p. V (work of expansion) 
 U = q – p. V or q = U + p. V, q,w are not state function. 
83 
 
 But U is state function. 
8. Enthalpy (H): At constant volume V = 0,  q
v
 = U 
 So H = U + p. V, q
p
 = H
2
 H
1
 = H 
 H = U + P. V. 
9. Relationship between q
p
, q
v
 i.e. H& U 
 It is H = U+ ng.RT or q
p
 = q
v + 
 ng.RT 
10. Exothermic and Endothermic reactions: H = –Ve for exothermic and H 
= +Ve for endothermic reaction i.e. evolution and absorption of heat. 
Eg C+O
2
  CO
2
 + 393.5 KJ, H = –393.5 KJ (exothermic) 
N
2
 + O
2
  2NO – 180.7 KJ, H = 180.7 KJ (Endothermic) 
11. Enthalpy of reaction (
r
H): The amount of heat evolved or absorbed when 
the reaction is completed. 
12. Standard Enthalpy of reaction (
r
H
0
) at 1 bar pressure and specific temp. 
(290K) i.e. standard state. 
13. Different types of Enthalpies of reactions: 
(i) Enthalpy of combustion (
c
H),  (ii) Enthalpy of formation (
f
H) 
(iii) Enthalpy of neutralization  (iv) Enthalpy of solution 
(v) Enthalpy of atomization(
a
H), (vi)Enthalpy of Ionisation (
i
H) 
(vii) Enthalpy of Hydration (
hyol.
H) (viii) Enthalpy of fusion (
fus.
H) 
(ix) Enthalpy of vaporization (
vap.
H) (x)Enthalpy of sublimation (
sub.
H) 
 (
sub.
H) = 
fus.
(H) - 
vap
(H) 
14. Hess’s Law of constant heat summation: The total amount of heat change is 
same whether the reaction takes place in one step or in several steps. 
 
i.e. H = H
1
 + H
2
 + H
3 
+ -------- 
84 
 
15. Bond enthalpy: It is amount of energy released when gaseous atoms 
combines to form one mole of bonds between them or heat absorbed when 
one mole of bonds between them are broken to give free gaseous atoms. 
Further 
r
H = B.E. (Reactants) - B.E. (Products) 
16. Spontaneous & Non Spontaneous Processes: A process which can take 
place by itself is called spontaneous process. A process which can neither 
take place by itself or by initiation is called non Spontaneous. 
17. Driving forces for spontaneous process: (i) Tendency for minimum energy 
state. (ii) Tendency for maximum randomness. 
18. Entropy (S): It is measure of randomness or disorder of system.  
i.e. Gas>Liquid>Solid.  
Entropy change ( S) = 
1 1
.) rev (
mol . K . J
T
q
 
19. Spontaneity in term of ( S) 
S
(total) 
= S
(universe)
 = S
(system)
 + S
(surrounding)
 
If S
(total) 
is +ve, the process is spontaneous. 
If S
(total)
 is –ve, the process is non spontaneous. 
20. Second Law of thermodynamics: In any spontaneous process, the entropy of 
the universe always increases. A spontaneous process cannot be reversed. 
21. Gibb’s free energy (G): defined as G = H – T.S & G = H – T. S (Gibb’s 
Helmholts equation) it is equal useful work i.e. - G = W
(useful)
 = W
(max.)
 
If G = ve, process is spontaneous. 
22. Effects of T on spontaneity of a process: G = H – T. S. 
(i) For endothermic process may be non spontaneous at law temp.