CBSE Class 11 Chemistry Thermodynamics Notes Set E

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 + ------

ΔU = U2 – U₁ or U_P – U_R & 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 μ 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  ΔU = q + w, w = –p. ΔV (work of expansion)

ΔU = q – p. ΔV or q = ΔU + p.ΔV, q,w are not state function. 

But U is state function.

8. Enthalpy (H): At constant volume V = 0, q_v = ΔU

So H = U + p. ΔV, qp = H₂ H₁ = ΔH

=>H = U + P. ΔV.

9. Relationship between qp, qv i.e. ΔH&ΔU 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+O₂  →CO₂ + 393.5 KJ, H = –393.5 KJ (exothermic)

N₂ + O₂ 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 (Δ_cH),                     (ii) Enthalpy of formation (Δ_fH)

(iii) Enthalpy of neutralization                         (iv) Enthalpy of solution

(v) Enthalpy of atomization(Δ_aH),                    (vi)Enthalpy of Ionisation (Δ_iH)

(vii) Enthalpy of Hydration (Δ_hyol.H)                (viii) Enthalpy of fusion (Δ_fus.H)

(ix) Enthalpy of vaporization (Δ_vap.H)             (x)Enthalpy of sublimation (Δ_sub.H)

          (Δ_sub.H) = Δ _fus.(H) -  Δ_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 =Δ _H1 + Δ_H2 + Δ_H3 + -------- 

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