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 = åH|products| - åH|reactants|

 where DH = Enthalpy change in a reaction åHproducts = Sum of enthalpies of formation of products åHreactants = 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 B  DH1 = Q1J B C  DH2 = Q2J C D  DH3 = Q3J

Then, DH = DH1 + DH2 + DH3

8. Some Conversions:

 1 Joule = 1 Nm = 107 ergs 1 Calorie = 4.184 J = 4.184 × 107 ergs 1 lit-atm = 24.22 cal

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