Two Phases at Equilibrium as a Function of Pressure and Temperature

The equations that describe equilibrium conditions between two phases of the same substance are derivable from the two laws of thermodynamics with the aid of the functions that we defined in the preceding chapter. Let us represent the equilibrium in a closed system at any given temperature and pressure by the equation 

As the system is at equilibrium at con stant temperature and pressure, any infinitesimal transfer of matter between Phase A and Phase B occurs with a change of zero in 

Chemical Thermodynamics Basic Concepts and Methods, Seventh Edition. By Irving M. Klotz and Robert M. Rosenberg 

As Equation (8.3) holds for any infinitesimal transfer drip whatsoever, the quantities in parentheses must equal zero and 

If the temperature and pressure are changed by amounts dT and dP such that the system reaches a new state of equilibrium, then the molar Gibbs functions of A and B change by amounts of dGA and dG- such that 

---

TWO PHASES AT EQUILIBRIUM AS A FUNCTION OF PRESSURE AND TEMPERATURE we obtain... 

---