Application of the Gibbs equations for the stability limit to the description of second-order phase transitions: General relations

The equation for the "stability limit" or spinodal, suggested by Gibbs, is directly related to second-order phase transitions, because the line of these transitions represents the merged spinodals of both interconverting phases. Therefore, it is the Gibbs equation that defines the line of second-order phase transitions. This equation and the known concepts of the order parameter are used to derive the basic analytical relations for the thermodynamic functions in the region of second-order phase transitions and to determine the most general characteristic regularities of these transitions.