# Top-rated ScreenCasts

Text Section | Link to original post | Rating (out of 100) | Number of votes | Copy of rated post |
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01.2 Molecular Nature of Temperature, Pressure, and Energy | Click here. | 84.4444 | 9 |
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? |

07.06 Solving The Cubic EOS for Z | Click here. | 83.3333 | 6 |
3. Using Preos.xlsx and Interpreting Output (11:38) (msu.edu) 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? |

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). |

10.01 - Introduction to Phase Diagrams | Click here. | 80 | 4 |
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: |

13.03 - NTRL | Click here. | 80 | 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)? |

18.09 - Sillen Diagram Solution Method | Click here. | 80 | 1 |
Sillen Diagram for Electrolyte Calculations (10:14) (msu.edu) Construction of a Sillien diagram involves several steps that are hard to follow from a textbook. This screencast goes through the steps of solving Example 18.5 from the Elliott and Lira textbook using the Sillen diagram. The problem asks for the pH of a solution that is 0.01 M NaOAc. |

10.10 - Mixture Properties for Ideal Solutions | Click here. | 80 | 1 |
10.9 - 10.12 Mixture Properties Overview (6:53) (msu.edu) This section of the text is thick with lots of equations. It may help to filter out the most important equations and results so that you have the perspective of the overall objectives of this section. There are a lot of equations in this section to show that the component fugacity in an ideal solution is simply the mole fraction multiplied by the pure component fugacity. In a liquid mixture, this is approximated as the mole fraction times the vapor pressure! This screencast goes on to preview the most important results of the next section to help you see the overall story. |

13.05 - UNIFAC | Click here. | 80 | 5 |
Unifac.xls Calculation of Bubble Temperature. (3 min) (LearnChemE.com) |

07.05 Cubic Equations of State | Click here. | 80 | 1 |
Intro to the vdW EOS. (LearnCheme.com, 5min) Provides a brief overview of the van der Waals (vdW) 1873 equation of state (EOS), which served as a prototype for EOS development for over 100 years. Note: the vdW EOS is just one conjecture of how equations of state for real fluids may be formulated. In reality, each fluid has its own unique EOS. The vdW model conjectures that the pressure is altered relative to the ideal gas by the presence of attractive forces and repulsive forces. Comprehension Questions: 1. Of the two parameters |

01.2 Molecular Nature of Temperature, Pressure, and Energy | Click here. | 77.8947 | 19 |

Molecular Nature of Internal Energy: Thermal Energy

This introduction to "thermal energy" elaborates on the ideal gas definition of temperature, which derives from the way that

PVis related to kinetic energy. ThisPVrelation can be easily understood in terms of an ultrasimplified model of ideal gas pressure. (uakron, 6min). Noting empirically from the ideal gas law thatPV=nRT, we are led to the derivation of Eqn. 1.1 (uakron, 5min, same as above). This result suggests counter-intuitive implications about the the ways that solid, liquid, and gas molecular velocities must be related. When applying Eqn. 1.1, you must be careful to keep your units straight, as illustrated in this sample calculation of molecular temperature for Xenon (Mw=131g/mol) (uakron, 5min). On a closely related note, we could perform a sample calculation of molecular pressure for Xenon using Eqn. 1.21.Comprehension Questions:

1. If two phases are in equilibrium (e.g. a vapor with a solid), then their temperatures are equal and the rate at which molecules leave the solid equals the rate at which molecules enter the solid. Which molecules are moving faster, solid or vapor? For simplicity, assume that the vapor is xenon and the solid is xenon. Hint: think about the exchange of momentum when the vapor molecules collide with the solid.

2. Compute the average (root mean square) velocity (m/s) of molecules at room temperature and pressure and compare to their speeds of sound. You can search the internet to find the speed of sound.

a. Argon

b. Xenon

3. Three xenon atoms are moving with (x,y,z) velocities in m/s of (300,-450,100), (-100,300,-50), (-200,-150,-50). Estimate the temperature (K) of this fluid.

4. Estimate the pressure of the xenon atoms in Q3 above in a vessel that is 4nm

^{3}in size.