Thermodynamic Fluid Stability and the Gibbs Free Energy

3 THERMODYNAMIC FLUID STABILITY AND THE GIBBS FREE ENERGY 

The total Gibbs free energy is given by (Walas, 1985 Prausnitz et al., 1986) 

The Hessian matrix of the Gibbs free energy [G] is useful in determining the stability of a given fluid phase. For a fluid phase to be stable the eigenvalues of [G] must be positive. The elements of this matrix are defined by 

The first two terms are the contribution to the G,y from the ideal Gibbs free energy, the last four terms represent the contribution from the excess Gibbs energy. For a binary system Eq. D.3.4 simplifies as follows  

The accompanying diskette contains Mathcad implementations of the examples that are worked out in detail in the text. Some of these files require only minimum modification in order to be useful for solving some of the exercises. It is necessary to purchase the Mathcad program in order to load these examples. 

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