Calculating activities from the phase diagram involving an intermediate compound using its entropy of formation

A new method for calculating activities of components from phase diagrams involving several intermediate compounds has been presented, in which only the entropies of formation of the intermediate compounds are required. It is expected that this method will be useful in situations where the free energy of formation, partial molar enthalpy and other thermodynamic data are not available. The application of this procedure to the Au−Bi and Mg−Si systems demonstrates that this method is feasible. Finally, activity values for the Au−Sb system are calculated by this method. JIAN-JUN WANG, former Student in the Department of Physical Chemistry, Beijing University of Iron and Steel Technology, Beijing, People's Republic of China.