# Top-rated ScreenCasts

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11.01 Modified Raoult's Law and Excess Gibbs Energy Click here. 20 1

Modified Raoult's Law and Excess Gibbs Energy (6:27) (msu.edu)

What are 'postive deviations' and 'negative deviations'? What are the 'rules of the game' for working with deviations from Raoult's law?

This screencast show the three main stages of modeling deviations from Raoult's law: 1) obtaining the activity coefficient from experiment; 2) fitting the activity coefficient to an excess Gibbs energy model; 3) using the fitted model to perform bubble, dew, flash calculations. These three stages are often jumbled up when first learning about activity coefficients, so explicit explanation of the strategy may be helpful.

08.07 - Implementation of Departure Functions Click here. 20 5

Helmholtz Example - Modified vdW EOS (uakron.edu, 13min) A sample derivation of the Helmholtz departure implicit in the Gibbs departure given Z = 1 + abρ/(1+)^3 - (9.5aρ/RT)/(1+aρ/RT). Note that the limits of integration matter for this EOS. The audio is inferior for this live video, but it responds to typical questions and confusion from students in the audience. Some students might find it helpful to hear the kinds of questions that students ask. The responses slow the derivation down so that no steps are skipped and key steps are reiterated multiple times. Just turn the volume up!
Comprehension questions:
1. Which part of this EOS is non-zero at the zero density limit of integration?
2. Is there a sign error on one of the terms in this video? Check the derivation independently.
3. Derive the Helmholtz departure given Z = 1 + 4bρ/(1-)2 - (9.5aρ/RT)/{1-a/bRT[1-4bρ+4(bρ)2]}.
4. Derive the Helmholtz departure given Z = 1 + 4bρ/(1-2) - (9.5aρ/RT){1+4/bRT[1-2(bρ)2]}/{1-a/bRT[1-4bρ+4(bρ)2]})/{1-a/bRT[1-4bρ+4(bρ)2]}

11.01 Modified Raoult's Law and Excess Gibbs Energy Click here. 20 1

Fitting One-Parameter Margules Equation (4:01) (msu.edu)

This screencast show application of the Stage I and Stage II calculations using experimental data and the one-parameter Margules equation. It is helpful to follow this screencast with the application of Stage III calculations described in the screencasts for Section 11.2.

08.07 - Implementation of Departure Functions Click here. 20 1

Helmholtz Example - Scott+TPT EOS. (uakron.edu) A sample derivation (8min) for the compressibility factor given that (A-Aig)TV/RT = -2ln(1-2ηP) - 18.7ηPβε/[1+0.36βεexp(-5ηP)]. This equation of state is a little complicated, but the derivation is no problem if you just go slow and steady. The remainder of this screencast shows a sample calculation (21min) to solve the resulting equation of state at a given value of pressure and temperature following the methodology of "visualizing the vdW EOS." This problem was adapted from an actual test problem. This screencast is live so the audio is inferior, but it gives insight into questions that real students have.
Comprehension Questions:
1. Derive an expression for the internal energy departure function of this EOS.
2. Is there a sign error on one of terms in this video? Check the derivation independently.
3. Derive the Z factor given (A-Aig)TV/RT = -2ln(1-2bρ) - (9.5aρ/RT)/{1-a/bRT[1-4bρ+4(bρ)2]}.

17.12 Energy Balances for Reactions Click here. 20 1

Equilibrium constants and adiabatic reactor calculations with Excel (uakron.edu, 6 min) We previously discussed adiabatic reactor calculations in Section 3.6 with application to the dimethyl ether process. At that time, we accepted the expression for equilibrium constant as given. In Chapter 17, we must recognize how to compute the equilibrium constant for ourselves. This presentation illustrates the calculations for Example 17.9. These kinds of calculations often occur in the context of an overall process, rather than in isolation. Therefore, the presentation shows how to apply Eqn 3.5b with pathway 2.6c to characterize the enthalpies of process streams and solve for the extent of reaction and adiabatic outlet temperature simultaneously.

Comprehension Questions:

1. Suppose the reactor inlet feed was: kmol/hr of 110 N2, 300 H2, 15NH3 and 16 CH4. Solve for the adiabatic reactor temperature and extent of reaction in that case.
2. Suppose the actual conversion was only 80% of the equilibrium conversion and the inlet feed was the same as given in part 1. Solve for the adiabatic reactor temperature and extent of reaction in that case.
3. Compute the stream attributes for this entire process assuming 85% of the equilibrium conversion and a feed (kmol/h) of 105 N2, 300 H2, 20 CH4 at 10bars and 200C. The distillation column operates at 10 bars with a partial condenser and splits of 99.99% on N2 and 2% on NH3. The recycle ratio is 19:1. Assume the compressors are 100% efficient and the reactor operates adiabatically with an inlet temperature of 400K and a pressure of 100bars. Report the molar flow rates of all outlet stream components.