# Top-rated ScreenCasts

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This video walks you through the process of transforming the M1/MAB model into the Scatchard-Hildebrand model using Excel (6min, uakron.edu) It steps systematically through the modifications to the spreadsheet to obtain each new model. You should implement the M1/MAB model before implementing this procedure.

Comprehension Questions:
1. Modify the M1/MAB spreadsheet to obtain Pxy diagrams with the Scatchard-Hildebrand, M2, and van Laar models.
2. Add Txy capability to each of the models.
3. Search for experimental data on the system ethanol+toluene. Modify your spreadsheets to plot the experimental data (points) on the same plot with the predictions. Which model (MAB or ScHil) provides the most accurate predictions when compared to data?

### Principles of Probability.

This is supplemental Material from "Molecular Driving Forces, K.A. Dill, S. Bromberg", Garland Science, New York:NY, 2003, Chapter 1. See the next three screencasts. This content is useful for graduate level courses that go into more depth or for students interested in more background on probability.

01.2 Molecular Nature of Temperature, Pressure, and Energy Click here. 84 10

Intermolecular Potential Energy (msu.edu) (7:11)

The intermolecular potential energy is distinct from the gravitational potential energy of the center of mass. Further, understanding of the potential energy relation with intermolecular force is important.

Comprehension Questions:

1. Molecules A and B can be represented by the square-well potential. For molecule A, σ = 0.2 nm and ε = 30e-22 J. For molecule B, σ = 0.35 nm and ε = 20e-22 J.  Sketch the potential models for the two molecules on the same pair of axes clearly indicating σ's and ε's of each species. Start your x-axis at zero and scale your drawing properly.  Make molecule A a solid line and B a dashed line. Which molecule would you expect to have the higher boiling temperature? (Hint: check out Figure 1.2.)

2. The potential, u(r), represents the work of bringing two molecules together from infinite distance to distance r. So, what is the force law between two molecules according to the Lennard-Jones potential model? Hint: W=∫F*dx

3. Sketch the potential and the force between two molecules vs. dimensionless distance, r/σ, according to the Lennard-Jones potential. Considering the value of r/σ when the force is equal to zero, is it greater, equal, or less than unity?

Bubble, Dew, Flash Concepts and the Lever Rule (4:01) (msu.edu)

Understanding what is present (known) and not present (unkown) for a given state of a system will help you decide which routine to use. Notation is introduced for liquids, vapor, and overall compositions. Also, the lever rule concept is used throughout the chemical engineering curriculum, but it is important to see how to use compositions for the lever rule.

Comprehension Questions:

1. Which variables are fixed and which do you need to find in each of the following:
a. Bubble temperature
b. Bubble pressure
c. Dew temperature
d. Dew pressure
e. Isothermal flash

UNIFAC concepts (8:17) (msu.edu)

UNIFAC is an extension of the UNIQUAC method where the residual contribution is predicted based on group contributions using energy parameters regressed from a large data set of mixtures. This screecast introduces the concepts used in model development. You may want to review group contribution methods before watching this presentation.

Comprehension Questions:

1. What is the difference between the upper case Θ of UNIFAC and the lower cast θ of UNIQUAC?

2. Suppose you had a mixture that was exactly the same proportions as the lower right "bubble" in slide 2. Compute ΘOH for that mixture.

3. Compare your value computed in 2 to the value given by unifac.xls.

3. Using Preos.xlsx and Interpreting Output (11:38) (msu.edu)
This screencast includes discussion of what we mean by the casual terminology 'three root region' and 'one root region', and how to interpret screen output. Also, the screencast spends time dicussing selection of stable roots using fugacity.

Comprehension Questions:

1. Is it possible to have a 1-root region below the critical temperature?

2. Is it possible to have a 3-root region above the critical temperature?

3. How does fugacity help us to identify the proper root to select?

4. Would argon at 5 MPa be in the 1-root or 3-root region?

Unifac.xls Calculation of Bubble Temperature. (3 min) (LearnChemE.com)
1. Estimate the activity coefficient of IPA in water at 80C and xw = 0.1.
2. Estimate the fugacity for IPA in water at 80C and xw =0.1.
3. Estimate the total pressure at 80C when xw =0.1.
4. Estimate the bubble temperature of IPA in water at 760mmHg and xw =0.1.

NRTL concepts (2:30) (msu.edu)

The concepts on the development of the NRTL activity coefficient model.

Comprehension Questions:

1. What value does the NRTL model assume for the coordination number (z)?
2. What does the acronym "NRTL" stand for?
3. What is the relation between τ12, τ21, and A12 of the M1 model when α12=0?
4. The NRTL model has one more parameter than the Wilson model. Which parameter is it and what is its default value?

15.04 - VLE calculations by an equation of state Click here. 80 1

PRMix.xlsx - Tutorial on use for bubble pressure (msu.edu) (10:06)

An overview of the organization of PRMix.xlsx, and a tutorial on the strategy to solve bubble pressure problems. Example 15.6 is worked in the screencast. After watching this screencast, you should be able to also solve dew or flash problems if you think about the strategy used to solve the problem. You may also be interested in a similar presentation from U.Colorado (learncheme, 6min).