One-Constant Margules To Represent Benzene - 2,2,4 - Trimethyl pentane

[studentsphere]

In the book, "Chemical, Biochemical, and Engineering Thermodynamics", 4th Edition - Stanley I. Sandler, Univ. of Delaware

On Pg. 435,the diagram (Fig 9.5-4) has been provided, which has been attached as a file. This represents the experimental activity coefficient data for the "benzene-2,2,4 trimethyl pentane mixture" and the correlation of these data obtained using the One-Constant Margules equation.


Illustration 9.5-1 asks to test the accuracy of the One-Constant Margules equation in correlating these data.

In the solution of this question, the book says that

"From the data presented in Fig 9.5-4 it is clear that the activity coefficient for benzene is not the mirror image of that for trimethyl pentane. Therefore, the one-constant Margules equation cannot be made to fit both sets of activity coefficients simultaneously".

I'm extremely confused as to why this diagram (Fig 9.5-4) is not considered to be a mirror image ?


A similar Figure (attached as fig2) has been described by the author as a mirror image. I consider both these diagrams to be identical


I hope someone can clarify my confusion

 

[Navin A S]

. The difference between the two diagrams is that in Figure 9.5-4, the activity coefficients for benzene and 2,2,4 trimethyl pentane are plotted against each other, while in Figure 2, the activity coefficient for benzene is plotted against the mole fraction of benzene in the mixture. This means that in Figure 9.5-4, the activity coefficients of the two components are not directly proportional to their mole fractions in the mixture, which is why it is not a mirror image.