Vanderwaals Constant-

source : askIITians

The vanderwaals constant are ‘a’ and ‘b’. These are characteristics of each gas and always depend on the nature of gas.

 units of vanderwaals constant ‘a’ and ‘b’ –

(A)  The pressure correction in vanderwaals equation is    an2/V2


   an2/V2 = unit of P

a = PV2/n2

a= Pressure X (volume)2/(mole)2

unit of a = atmosphere . litre2/mole2

unit of a = atmosphere . litre2 .mole-2


atmosphere. dm6. mole-2

of unit of P = Newton/meter2 = N/m2 or Nm-2 (SI unit)

V = meter3

unit of a = newton meter-2.meter6/mole2 = Nm-2m6/mole2

unit  of a = Nm4 mole-2

B) Effective volume for  ‘n’ moles of gas is ‘ nb’.

V= nb


b= Volume / mole

Unit of b = litre/mole = litre mole-1  OR   m3 mole-1 (SI unit)