# Top-rated ScreenCasts

Text Section | Link to original post | Rating (out of 100) | Number of votes | Copy of rated post |
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04.03 The Macroscopic View of Entropy | Click here. | 20 | 1 |
Once we establish equations relating macroscopic properties to entropy changes, it becomes straightforward to compute entropy changes for all sorts of situations. To begin, we can compute entropy changes of ideal gases (learncheme, 3 min). Entropy change calculations may also take a more subtle form in evaluating reversibility (learncheme, 3min). Comprehension Questions: 1. Nitrogen at 298K and 2 bars is adiabatically compressed to 375K and 5 bars in a continuous process. (a) Compute the entropy change. (b) Is this process reversible, irreversible, or impossible? |

11.05 - Modified Raoult's Law and Excess Gibbs Energy | Click here. | 20 | 2 |
Extending the M1 derivation of the activity coefficient to multicomponent mixtures (uakron.edu, 14min) is straightforward but requires careful attention to the meaning of the subscripts and notation. It is a good warmup for derivations of more sophisticated activity models. This presentation begins with a brief review of the M1 model and its relation to the Gibbs excess function, then systematically explains the notation as it extends from the binary case to multiple components. Comprehension Questions |

03.6 - Energy Balance for Reacting Systems | Click here. | 20 | 1 |
In case you need a little extra help on energy balances after iterating mass balances, this video walks you through the process. (8min, uakron.edu) for the same process flow diagram related to dimethyl ether synthesis. Comprehension Questions: 1. Choose any process flow diagram from your material and energy balances (MEB) textbook that has a recycle stream. Solve the problem using this technique and compare to the answer you obtained in MEB class. Estimate stream enthalpies for every stream and compute the overall energy balance of all product streams to all feed streams. Does the process require net heat addition or removal? |

05.2 - The Rankine cycle | Click here. | 20 | 1 |
Rankine Example Using Steam.xls (uakron.edu, 15min) High pressure steam (254C,4.2MPa, Saturated vapor) is being considered for application in a Rankine cycle dropping the pressure to 0.1MPa; compute the Rankine efficiency. This demonstration applies the Steam.xls spreadsheet to get as many properties as possible. Comprehension Questions: 1. Why does the proposed process turn out to be impractical? 2. What would you need to change in the process to make it work? Assume the high and low temperature limits are the same. Be quantitative. 3. What would be the thermal efficiency of your modified process? |