Fugacity coefficient physical interpretation

In 6.2.4 we showed the similarities that occur in the fugacity ratios that define the fugacity coefficient, the activity, and the activity coefficient, and in 6.3 those quantities were given physical interpretations. In this section we summarize certain generalized expressions that relate the fugacity to measurables. Many such relations can be written, but only five forms are in common use. 

Usually we c culate the fugacity through the i gacity coefficient. Before, however, we discuss how the fugacity coefficient is calculated, let us consider a physical interpretation of fugacity. 

This result for the fugacity coefficient can be interpreted through our physical understanding of the van der Waals parameters, a and fc. If a and b are negligible, we get attractive interactions dominate, the parameter a will most influence the system behavior. The third term on the right-hand side will cause... 

---