Derivation of critical constants from the Van der Waals contents:
Van der Waals equation is,
From this equation, the values of critical constant PCVC and TC arc derived in terms of a and b the Van der Waals constants.
The above equation (4) is an cubic equation of V, which can have three roots. At the critical point. all the three values of V are equal to the critical volume VC .
i.e. V = VC .
As the equation (4) is identical with equation (7), comparing the ‘V’ ternis in (4) and (7),
When equation (12) is substituted in (10)
Critical constant a and b can be calculated using Van der Waals Constant as follows:
