NetLogo Models Library:
This model follows on the Simple Kinetics 2 model. In Simple Kinetics 2, we saw how changes to variables such as temperature, volume, and concentration affected the rate at which a chemical reaction reached an equilibrium state. Here we model the same phenomenon based upon a physical separation.
This model investigates some laboratory methods that chemists use to purify chemicals. Most of these methods are based upon physical properties of molecular separation. The same principles that affect chemical equilibrium affect physical equilibrium as well. By changing the variables of temperature, volume, and concentration, we can affect not only the speed at which a system reaches equilibrium, but also the nature of the distribution ratio. In this model, we watch how these factors affect the physical distribution of red molecules that are considered "dissolved" in a blue solvent.
Setup the model by pressing either the SETUP-RANDOM or the SETUP-SIDE buttons at the top of the Interface tab. SETUP-RANDOM distributes all the molecules randomly around the world. SETUP-SIDE distributes the blue molecules evenly, while placing the red molecules on the right side of the world.
Press GO to watch the molecules move about the world as they achieve equilibrium. The plot tracks the relative concentrations of each color molecule on each side of the central divider. If the red line dips below 0, there are more red molecules on the left side of the divider than on the right. If it rises above 0, there are more red molecules on the right side of the divider than on the left. The blue line plots the same relationship for blue molecules.
You can add more red molecules to the right side of the world by pressing ADD RED.
Similarly, you can shrink or expand the right side of the box with the buttons SHRINK RIGHT and EXPAND RIGHT, respectively.
Finally, to change the size of the connection window, move the WINDOW slider to your desired size and then press the CHANGE WINDOW button.
Pay attention to the plot and compare it what you see in the world. Is there an equal number of blue and red molecules on each side of the divider according to the plot and according to what you see in the view?
Run the model with several different states for each variable. Do you observe similar equilibrium effects to those seen in Simple Kinetics 2? Are there significant differences?
Does the temperature affect the system in the same way it affected the chemical reaction in Simple Kinetics 2? Why or why not?
How does changing the concentration affect the rate at which the molecules achieve equilibrium? Does this make sense?
The system we have established here always comes to an approximately identical equilibrium state, no matter how you change the variables. In the lab, this is not useful to chemists, who want to separate one type of molecule from another. Can you extend the model to separate all of the red molecules from the blue molecules?
Try adding another color of molecule to the system and randomly distributing all the molecules around the world. Can you devise a way to separate the new molecules from the red molecules?
Add a slider that allows you to alter the temperature of the system. Think about what effect cooling and heating the system would have on the molecules. Be sure to include a command in the procedures window that will execute your proposed effect.
Simple Kinetics 1 Simple Kinetics 2
Thanks to Mike Stieff for his work on this model.
If you mention this model or the NetLogo software in a publication, we ask that you include the citations below.
For the model itself:
Please cite the NetLogo software as:
Copyright 2001 Uri Wilensky.
This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc-sa/3.0/ or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.
Commercial licenses are also available. To inquire about commercial licenses, please contact Uri Wilensky at firstname.lastname@example.org.
This model was created as part of the projects: PARTICIPATORY SIMULATIONS: NETWORK-BASED DESIGN FOR SYSTEMS LEARNING IN CLASSROOMS and/or INTEGRATED SIMULATION AND MODELING ENVIRONMENT. The project gratefully acknowledges the support of the National Science Foundation (REPP & ROLE programs) -- grant numbers REC #9814682 and REC-0126227.