[mrusnak]

P=(RT)/V - B/(V^2) + C/(V^3)

I understand the concept of critical behavior, but how does the previous equation lead to critical behavior? What I guess I don't understand is what are the parameters for critical behavior?

[Hunt]

If you look at the isotherms of a real gas you'll notice that at the critical point ( point of inflection ) the 1st and 2nd derivatives are equal to zero. This is the criteria for critical behaviour. In this case you set :

(dP/dV)_T = 0

(d²P/dV²)_T = 0

If the two equations can be solved for some paramaters ( as in here 'B' and 'C' ) then a critical behaviour is predicted by the such an equation of state. For example take PV=kNT , obviously no critical behaviour exists.

Ofcourse this is one method that relies on calculus , and there are other methods that are algebraic but not so much used.