NetLogo User Community Models
by Mitchell Hull (Submitted: 03/13/2004)
WHAT IS IT?
RELATIONSHIP BETWEEN TEMPERATURE AND KINETIC ENERGY OF MOLECULES
This model demonstrates the connection between chemical reactions and the free energy or heat of the system. Chemical reactions often need an initial input of energy to start the reaction. While the reactants of a reaction may be plentiful and often collide, they may not collide with enough force to trigger the reaction. The Kinetic Energy (or speed) of molecules and therefore the force of a collision can be increased by increasing the temperature of the surroundings (ambient temperature).
This model demonstrates this concept. The molecules move at a speed proportional to their surroundings and collisions are calculated based on molecular speed and the angles of their trajectory (i.e. to particles colliding head on do so with more fore than particles that scrape by each other).
EXOTHERMIC AND ENDOTHERMIC REACTIONS
When reactants come together with enough Kinetic Energy they will react to form product(s). In most reactions, heat is released into the system (Exothermic) or absorbed from the system (Endothermic) to create the product. This in turn will gradually raise or lower the ambient temperature of the system.
This model reflects this and the system will heat or cool depending on whether the reaction is Exothermic or Endothermic. The model does not immediately heat the entire system the temperature change is first local and then dissipates into the surroundings gradually heating the system. As a result, there will exist local hot and cold pockets in our model.
MORE ABOUT HEAT IN A SYSTEM
Heat tends to escape from a system. A perfectly insulated system will keep all of the energy released within the system. Conversely, a perfectly non-insulated system will lose all of the energy released within the system.
HOW IT WORKS
Two reactants will move within the system and react according to user's set parameters and mouse actions. The program will plot the number of reactants, products and the heat of the system.
HOW TO USE IT
setups: Preprogrammed setups for the models. See "THINGS TO TRY" section for description. If user deviates from preprogrammed setups, (s)he must select "USER" in this menu.
setup: Sets up the model based on the user defined variables or selected "setup".
go: Starts and Stops the model.
mouse: The user can heat or cool localized temperature by clicking down on an area with the mouse. Holding the mouse down will continue to affect the system as will a mouse drag. This function is used in combination with the mouse-temp-effect variable.
mouse-temp-effect (slider): Sets the amount of heating or cooling the mouse can do on the system.
MORE ADVANCED USE
ambient-temperature (slider): Sets the ambient temperature of the system. It will increase on its own in a system reacting exothermically.
reactant-number (2 sliders): Sets the initial number of reactants in the system.
reactant-threshold (slider): Sets the force (energy) threshold of colliding reactants needed to react and become a product.
energy-released: Sets the amount of heat absorbed or released into the system. Setting this greater than zero creates Exothermic Reactions. Setting this less than zero creates Endothermic Reactions.
EVEN MORE ADVANCED USE
system-insulation: Sets the insulation of a system. The maximum value of 10 will keep all of the heat release by reactions or mouse clicks in the system. A model set to 0 will never heat or cool.
heat-diffusion (slider): Sets the rate of diffusion of heat into the system.
color-sensitivity (slider): Sets the heat coloring function's sensitivity to the average temperature. A high value will make the coloring less sensitive relative to the ambient temperature.
coloration: "RED AND BLUE" is the best selection for noticing individual reactions-- especially if you plan to display endothermic reactions, which are nearly unnoticeable in the "RAINBOW 1" and "RAINBOW 2" algorithms. However, the "RAINBOW" coloration schemes could be more interesting as models that show heat dispersion. "RAINBOW 1" AND "RAINBOW 2" are nearly identical, however the background "RAINBOW 2" is not normalized to the ambient temperature and therefore changes color as the ambient temperature increases.
THINGS TO NOTICE
Molecules move noticeably faster in hotter patches and will slow again in cooler patches.
Heat patches with the mouse and watch as the molecules seem to flee this area. They are really just speeding up.
Calculations of the force of impact between two molecules are based on the speed and angle of the molecules.
The molecules are modeled after the chemical reaction of hydrogen and oxygen to form water. However, the molecules are not named for this reaction because the chemical reaction shown is not balanced and can be endothermic.
Cooling is less noticeable: we can only make an area so cold (0). So localized effects, which are dissipated, are not as visual as heating which can create temperature differences several hundred degrees hotter than the average temperature.
The program will color the local environment (roygbiv scale: red = hot; blue = cold) of the system relative to the average temperature for the "RAINBOW" coloration models. This means that a red-hot patch in a system with an average temperature of 5 will be less than a cool-green/blue patch in a system with an average temperature of 100. The relative nature of the color scale can be altered by the color-sensitivity slider.
THINGS TO TRY
USER: User defined setup. Use this choice to alter predefined setups.
DEFAULT: This model is a good place to start when experimenting with "USER" setup and mouse temperature effects. Its variables are set to benign levels that will do little without user input.
EXPLOSION: The model is an explosion waiting to happen. Use your mouse to set it off. Observe the reaction and especially the plots-- this setup creates a great curve.
SPONTANEOUS: The model is similar to the defaul model, but the reaction-threshold is set lower and therefore we will see more reactions.
ENDOTHERMIC: Perhaps the most interesting model. Set to model an endothermic reaction, the reaction needs a catalyst or booster (in the form of mouse heating) to start the reaction. It makes for an interesting combination of hot and cold effects. NOTE: this model should be used with "RED AND BLUE" for best results.
LIMITED REACTANT: Model shows the importance of both reactants in the reaction. Good younger students.
EXTENDING THE MODEL
The colorations scheme could be added to and improved.
Other Chemistry sample models especially those in the Chemical Reactions folder.
CREDITS AND REFERENCES
Thanks to Mitchell Hull for his creation of this model
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