<P> Although the material constant a and b in the usual form of the van der Waals equation differs for every single fluid considered, the equation can be recast into an invariant form applicable to all fluids . </P> <P> Defining the following reduced variables (f, f are the reduced and critical variable versions of f, respectively), </P> <Dl> <Dd> p R = p p C, v R = v v C, and T R = T T C (\ displaystyle p_ (R) = (\ frac (p) (p_ (C))), \ qquad v_ (R) = (\ frac (v) (v_ (C))), \ quad (\ hbox (and)) \ quad T_ (R) = (\ frac (T) (T_ (C)))), </Dd> </Dl> <Dd> p R = p p C, v R = v v C, and T R = T T C (\ displaystyle p_ (R) = (\ frac (p) (p_ (C))), \ qquad v_ (R) = (\ frac (v) (v_ (C))), \ quad (\ hbox (and)) \ quad T_ (R) = (\ frac (T) (T_ (C)))), </Dd>

Van der waals equation for real gases pdf