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Using One-Constant Margules To Represent "benzene - 2,2,4 - Trimet


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#1 process.eng

process.eng

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Posted 01 April 2010 - 04:00 AM

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

Attached Files



#2 MrShorty

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Posted 01 April 2010 - 11:29 AM

I think I see where your confusion lies.

You are correct, in that the drawn curves in Fig 9.5-4 appear to be mirror images of each other. What do these curves represent? One constant Margules correlations, so they will naturally appear symmetric.

An exercise I might suggest that should lead you to the correct conclusion. Take the figure and locate the dots representing the actual measured data. Hand draw a curve through those dots, ignoring the existing curves. Does this "eyeball" fit appear to be symmetric?




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