Excess Nature of Interfacial Thermodynamic Quantities The Gibbs Dividing Plane

9 EXCESS NATURE OF INTERFACIAL THERMODYNAMIC QUANTITIES THE GIBBS DIVIDING PLANE 

Consider a two-phase system containing the homogeneous phases a and P divided by a flat interface. Each phase is thermodynamically characterized by its variables of state. The crossing over from a to P takes place over a region of finite thickness. In this transition region the intensive thermodynamic quantities change gradually from 

Having established the position of the Gibbs dividing plane, the volumes of a and P, F , and are fixed and because the dividing plane is volumeless, the total volume V of the system is given by 

After having fixed F and VP, any other extensive property Y of the system is assumed to be made up of its contributions from a, P, and the interface o, 

FIGURE 3.4 Gibbs dividing plane between a liquid and a vapor, p is the density of the phase indicated. 

---