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MHT-CET : Chemistry Entrance Exam

MHT - CET : Chemistry - Chemical Thermodynamics and Energetics Formulae Page 1

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1. Work obtained in an isothermal and reversible process (against constant pressure):

 

 

W

= P(V2 - V1)

 

= P D V

 

where, W

= Work done

P

= Pressure

V1

= Initial volume

V2

= Final volume

DV

= Change in volume

 

2. Maximum work obtained in an isothermal, reversible expansion of gas:

 

Wmax = 2.303 nRT log

V2

V1

 

Wmax = 2.303 nRT log

P1

P2

 

where, Wmax =

Maximum work done

n =

Number of moles

=

Weight of the gas in kg

Molecular weight in kg

R =

Gas constant

=

8.314 JK-1 mol-1

T =

Temperature in kelvin

V1=

Initial volume

V2=

Final volume

P1=

Initial pressure

P2=

Final pressure

 

3. First Law Of Thermodynamics:

 

Q = DE + W
i.e. Q =
DE + PDV

where, Q =

Amount of heat absorbed

DE =

Change in internal energy

W =

Work done

P =

Pressure

DV =

Change in volume

 

 4. Enthalpy And Enthalpy Changes:

 

DH = DE + PDV
DHp = DHv + PDV, for gaseous reactions

where, DH =

Change in enthalpy

DE =

Change in internal energy

P =

Pressure

DV =

Change in volume

DHp =

Heat of reaction at constant pressure

DHv =

Heat of reaction at constant volume

For a reaction involving change in number of moles,
DH = DE + DnRT or Qp = QV + DnRT

where, D n =

Change in the number of moles of gaseous reactants and products

=

(Number of moles of gaseous products) - (Number of moles of gaseous reactants)

R =

Gas constant

T =

Temperature in kelvin

 

5. Kirchoff's Equation:

 

 

DH2 = DH1 + DCp (T2 - T1)

 

6. Thermochemistry:

 

DH = H|products| - H|reactants|

where DH

= Enthalpy change in a reaction

Hproducts

= Sum of enthalpies of formation of products

Hreactants

= Sum of enthalpies of formation of reactants

 

7. Hess's Law:

 

If a chemical reaction, A D; DH = QJ is carried out as follows:

A DH1

= Q1J

B DH2

= Q2J

C DH3

= Q3J

Then, DH = DH1 + DH2 + DH3

 

8. Some Conversions:

 

  1. 1 Joule = 1 Nm = 107 ergs
  2. 1 Calorie = 4.184 J = 4.184 107 ergs
  3. 1 lit-atm = 24.22 cal

 

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