Excess Gibbs Energy and Activity Coefficient Equations

3 EXCESS GIBBS ENERGY AND ACTIVITY COEFFICIENT EQUATIONS 

To find the above relations in terms of mol fraction and excess Gibbs energy g per mol of solution, we divide each part of Eq. 9.3 by Wj-, finding 

In most activity coefficient calculations we use g /RT as die dimensionless correlating variable, which simplifies the computations an additional correlating parameter, g / RTXaXb), has advantages that will become clear after the next example. 

Example 9.2 Calculate and plot g /RT and (g /RTxaXb) for the acetone-water solution at 1 atm pressure, using the VLE data from Example 8.2. 

FIGURE 9.3 Calculated values of lOg /RT and (g /RTxaXb) plotted as a function of the mol fraction of acetone in the liquid phase for acetone and water. The g /RT values are multiplied by 10 to make the values more or less the same size. 

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