# Top-rated ScreenCasts

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07.09 -The Molecular Basis of Equations of State: Concepts and Notation Click here. 93.3333 3

Nature of Molecular Interactions - Macro To Nano(8min). (uakron.edu) Instead of matching the critical point, we can use experimental data for density vs. temperature from NIST as a means of characterizing the attractive energy and repulsive volume. A plot of compressibility factor vs. reciprocal temperature exhibits fairly linear behavior in the liquid region. Matching the slope and intercept of this line characterizes two parameters. This characterization may be even more useful than using the critical point if you are more interested in liquid densities than the critical point. In a similar manner, you could derive an EOS based on square-well (SW) simulations and use the SW EOS to match the NIST data(11min), as shown in this sample calculation of the ε and σ values for the SW potential. In this lesson, we learn how to characterize the forces between individual atoms, which may seem quite unreal or impractical when you first encounter it. On the other hand, "nanotechnology" is a scientific discipline that explores how the manipulation of nanostructure is now quite real with very significant practical implications. "The world's smallest movie" shows dancing molecules, (IBM, 2min) demonstrating the reality of molecular manipulation, and the accompanying text explains some of the practical implications. Along similar lines, researchers at LLNL and CalTech have developed 3D printers that can display "voxels" (the 3D analog of pixels) of ~1nm3. That's around 10-100 atoms per voxel. Since 2013-14, chemical/materials engineers have been building nanostructures (TEDX, 13min) in the same way that civil engineers build infrastructure.
Comprehension Questions:
1. What does the y-intercept represent in a plot of compressibility factor vs. reciprocal temperature?
2. What parameter does the y-intercept help to characterize, b or ε?
3. What does the x-intercept represent in a plot of compressibility factor vs. reciprocal temperature?
4. What parameter does the x-intercept help to characterize, b or ε?
5. Apply the SW EOS given in the second video to the isochore at 16.1 mol/L. Do you get the same values for ε/k and σ? Explain.

Solid-Liquid Equilibria using Matlab (7:17) (msu.edu)

The strategy for solving SLE is discussed and an example generating a couple points from Figure 14.12 of the text are performed. Most of the concepts are not unique to UNIFAC or MATLAB.

14.09 - Numerical procedures for binary, ternary LLE Click here. 90 2

LLE Calculations: UNIFAC from Actcoeff.xlsx Calculation of LLE. (5 min) (LearnChemE.com)
See also - Supplement on Iteration of LLE with Excel and Matlab. Hints on converging LLE using Excel with the method presented in the textbook. For details, see

Departure Functions: PREOS.xls Compressor and OVC Design (11min) (uakron.edu) Redesign the ordinary vapor compression cycle (OVC) using propane as discussed in Chapter 5, this time applying PREOS.xls instead of the chart. In this sample calculation, the cycle operates from -100F in the evaporator with a compressor that takes the saturated vapor from the evaporator to 10 bars and 180F. With this procedure, applying PREOS.xls could be adapted to any compound in the database, not just propane. So PREOS.xls represents the equivalent of charts for roughly 200 compounds, and that's just what it can do for pure fluids.
Comprehension Questions: Assume a reference state of the saturated liquid at 1 bar. Use Eqn. 2.47 (SCVP eq) to estimate saturation conditions.
1. Compute the enthalpy (J/mol) of saturated vapor N2O at -100F.
2. Compute the enthalpy (J/mol) of saturated liquid N2O at 80F.
3. Compute the enthalpy (J/mol) of N2O at 60 bars and 350F.
4. Compute the COP for this OVC cycle.

Liquid fugacity relative to vapor fugacity. (LearnChemE, 5 min) This screencast shows a sample derivation and sample calculation for the vapor equation of state given by: Z = 1-0.01P, solve for: (a) the vapor fugacity at 500K and 30 bar (b) the liquid fugacity in equilibrium with the same vapor at 500K and 30bar (c) the liquid fugacity at 500K and 60 bar. Data: VL = 25 cm3/mol.

Comprehension Questions:

1. How much did raising the pressure to 60 bar change the liquid fugacity (bars) (+/- 1%)?
2. Estimate the fugacity (bars) of the vapor at 500 K and 60 bar and compare it to the liquid. Which is smaller? Which state do you think best characterizes the fluid (ie. V or L)?
3. Estimate the fugacity (bars) of n-pentane vapor at 30 bar and 460 K by Eqn. 7.5.
4. Assuming VL=229cm3/mol, estimate the fugacity of liquid n-pentane at 460K and 600bar.

P-V and P-T diagrams (LearnChemE.com) (5:52) Describes distinctions and trends between solid, vapor, liquid, gas.

Activity Coefficient Calculations in Matlab (6:12) (msu.edu)

An overview of the strategy of placing the activity coefficient models in a single folder, how the gammaModels .m files are used with scalars and vectors, and how to use the Matlab 'addpath' command to run the code from any folder on your computer.

Dew Pressure (7:41) (msu.edu)

The culmination of the activity coefficient method is application of the fitted activity coefficients to extrapolate from limited experiments in a Stage III calculation. The recommended order of study is 1) Bubble Pressure; 2) Bubble Temperature; 3) Dew Pressure; 4) Dew Temperature. Note that an entire Pxy diagram can be generated with bubble pressure calculations; no dew calculations are required. However, many applications require dew calculations, so they cannot be avoided. The dew calculations are more complicated than bubble calculations, because the liquid activity coefficients are not known until the unknown liquid mole fractions are found. This screencast describes the procedure and how to implement the method in Matlab or Excel.

Molecular Nature of U and PV=RT (msu.edu) (5:04)

Internal energy is the sum of molecular kinetic energy and intermolcular potential energy, which leads to the relation between internal energy and temperature for an ideal gas. Also, the ideal gas law can be derived by incoporating the relation between kinetic energy and temperature with the force due to the molecules bouncing off the walls.

Comprehension question:
One mole of Xenon molecules (MW=131g/mol) is flying back and forth in the x-direction of a three-dimensional cube of 1m³ volume with zero velocity in the y- or z- directions. The velocity of every molecule is 300 m/s. Estimate the pressure (MPa) in the x- and y- directions.