# cbse class 11 physics thermodynamics important question and sample paper

Topics: Thermodynamics, Enthalpy, Entropy Pages: 26 (2369 words) Published: October 15, 2013
CHAPTER 6
THERMODYNAMICS”
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 = Ee + En + Ec + Ep + Ek + -----U = U2 – U1 or UP – UR & U is state function and extensive properly. If U1 > U2 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

7.

J).

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.
82

But U is state function.
8.

Enthalpy (H): At constant volume V = 0,

qv = U

So H = U + p. V, qp = H2 H1 = H
H = U + P. V.
9.

Relationship between qp, qv i.e. H& U
It is H = U+ ng.RT or qp = qv +

10.

ng.RT

Exothermic and Endothermic reactions: H = –Ve for exothermic and H = +Ve for endothermic reaction i.e. evolution and absorption of heat. Eg C+O2
N2 + O 2

11.

CO2 + 393.5 KJ, H = –393.5 KJ (exothermic)
2NO – 180.7 KJ, H = 180.7 KJ (Endothermic)

Enthalpy of reaction ( rH): The amount of heat evolved or absorbed when the reaction is completed.

12.

Standard Enthalpy of reaction ( rH0) at 1 bar pressure and specific temp. (290K) i.e. standard state.

13.

Different types of Enthalpies of reactions:
(i)

Enthalpy of combustion ( cH),

(ii)

Enthalpy of formation ( fH)

(iii) Enthalpy of neutralization

(iv)

Enthalpy of solution

(v) Enthalpy of atomization( aH),

(vi)Enthalpy of Ionisation ( iH)

(vii) Enthalpy of Hydration (

(viii) Enthalpy of fusion (

hyol. H)

(ix) Enthalpy of vaporization (
(
14.

sub.H)

=

fus.(H)

-

vap.H)

fus.H)

(x)Enthalpy of sublimation (

sub.H)

vap(H)

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 = H1 + H2 + H3 + -------83

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

16.

rH

= B.E. (Reactants) - B.E. (Products)

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) =

19.

q ( rev.)
T

J.K 1 .mol

1

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...