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CHAPTER 6THERMODYNAMICS”
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 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.
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, 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 + 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+O2 CO2 + 393.5 KJ, H = –393.5 KJ (exothermic)
N2 + O 2 2NO – 180.7 KJ, H = 180.7 KJ (Endothermic)
11. 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 ( 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 = H1 + H2 + H3 + --------
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