Real Gases at High P and T Conditions

Values of critical temperature and critical pressure for gaseous species of geochemical interest are listed in table 9.3. 

The values allow the calculation of fugacity and, thence, the chemical potential of the gaseous component at the P and T of interest, applying 

As we have already seen, the universal chart of gases assumes that all gaseous species exhibit the same sort of deviation from ideal behavior at the same values of 7, and V. This fact, known as the principle of corresponding states, is analytically expressed by the deviation parameter (or compressibility factor ) Z. For n =,  

Confirmation of the validity of the principle of corresponding states is shown in figure 9.4A, where we see the analogies in the reduced isotherms of H2O, CO2, and N2 according to reduced pressure. However, figure 9.4B shows that the principle of corresponding states is only an approximation of actual behavior in the vicinity of the critical point in the case of H2O, there are in fact discrepancies between predicted and actual behavior. 

Deviation parameter Zg is operationally expressed as a virial expansion on P or V  

---