Vanderwaals Constant

Vanderwaals Constant-
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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

so,

   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

OR

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=V/n

b= Volume / mole

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