Heat and Thermodynamics

5.8 Merits and Demerits of Van der Waals′ Equation

In spite of the fact that Van der Waals’ equation has been very helpful in understanding many of the properties of real gases, the evaluation of critical constants, the derivation of the equation of corresponding states, the continuity of the gaseous to the liquid state, when it is subjected to experimental verification, we find considerable discrepancies. These are:

1. We have seen that for CO₂, the curves drawn from Van der Waals’ equation do not coincide with the experimental curves of Andrews. Marked discrepancy is observed for isothermals below the critical one where Van der Waals’ equation gives one maxima and one minima.
2. Van der Waals’ equation supposes a and b to be constants, but these ...