# 10.07 - Nonideal Systems

### Visualizing Pxy Phase Diagrams in Excel

This screencast shows how to quickly visualize Pxy phase diagrams for nonideal systems using Excel (5min, uakron.edu). These sample calculations for methanol+benzene apply the simplest nonideal solution model: ΔHmix = A12*x1*x2. Rigors of this model are discussed in Chapter 11. Nevertheless, its basic elements are simple enough that they can be understood in Chapter 10. When x1=0 or x2=0, a pure fluid is indicated, corresponding to no mixing and zero heat of mixing. When A12=0, the ideal solution approximation is recovered. When A12>0, the model indicates an endothermic interaction (like 2-propanol+water, Fig. 10.8c), giving rise to "positive deviations from Raoult's Law." When A12<0, the model indicates an exothermic interaction (like acetone+chloroform, Fig. 10.9c), giving rise to "negative deviations from Raoult's Law." With this spreadsheet, you can quickly change your components and A12 values to see how the phase diagram changes and gain "hands-on" familiarity with the principles discussed in Section 10.7.

Note: This is a companion file in a series. You may wish to choose your own order for viewing them. For example, you should implement the first three videos before implementing this one. Also, you might like to see how to quickly visualize the Txy analog of the Pxy phase diagram. If you see a phase diagram like the ones in section 11.8, you might want to learn about LLE phase diagrams. The links on the software tutorial present a summary of the techniques to be implemented throughout Unit3 in a quick access format that is more compact than what is presented elsewhere. Some students may find it helpful to refer to this compact list when they find themselves "not being able to find the forest because of all the trees."

Comprehension Questions:
1. Make a Pxy diagram for cyclohexane+toluene at 80C and A12=200. What kind of system is this?
2. Make a Pxy diagram for cyclohexane+benzene at 80C and A12=200. What kind of system is this?
3. Why does the system's qualitative behavior change so much when the components and model parameters are changed so little?

### Nonideal Mixtures (4:58) (msu.edu)

Nonideal Mixtures (4:58) (msu.edu)

Raoult's law is an easy way to calculate VLE, but it is inaccurate for most detailed VLE calculations. This screencast provides an overview of the problems, and introduces the concept of an azeotrope. The VLE K-ratio is shown to be less than one or greater than one dependenting on the overall system concentration relative to the azeotrope composition where K=1. The concept of positive and negative deviations is introduced.

### Visualizing Txy Phase Diagrams in Excel

Txy phase diagrams are basically the mirror image of Pxy diagrams for VLE because a high pressure indicates a liquid but a high temperature leads to a vapor. We can visualize Txy diagrams for VLE (uakron, 7min) in much the same way as for Pxy diagrams. Txy diagrams have the additional advantage of illustrating the onset of liquid-liquid equilibrium (uakron, 6min) at low temperatures. We discuss liquid-liquid equilibria (LLE) calculations in Chapter 14, but it is useful to learn your way around a complete phase diagram (uakron, 10min) properly from the beginning, instead of learning bits and pieces here and there.The first two videos illustrate sample calculations for methanol+benzene. Both of these are revisited in later chapters. The last video illustrates a sample quiz/test question about interpreting a phase diagram.

Comprehension Questions:

Referring to the phase diagram for ethyl acetate+water (cf. Figure 14.4) identify the phase nature (V, L, V+L, or L+L), phase composition(s), and phase amount(s) for the following points:
A. T = 360, xE = 0.7
B. T = 360, xE = 0.3
C. T = 340, xE = 0.7
D. T = 340, xE = 0.9