Question

Demonstrate that Eqs. (2.6a) and (2.6b) are valid for a substance, obeying the Van der Waals equation, in critical state. Instruction. Make use of the fact that the critical state corresponds to the point of inflection in the isothermal curve p(V).

Answer 1

The Vandar Waal's equation can be written as (for one mole)

Solving these simultaneously we get on  division

This is the critical molar volume. Putting this back

From these we see that