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NetLogo User Community Models
## WHAT IS IT?
This model demonstrates a basic combustion reaction, using methane as one of the reactants. Generally, combustion reactions consist of a hydrocarbon reacting with oxygen to form carbon dioxide and water. These reactions can occur spontaneously, or require energy in the form of heat to get started. The energy required to start a reaction is called the activation energy.
The combustion of methane in this model can be described with the following equation:
> CH<sub>4</sub> + 2O<sub>2</sub> —> CO<sub>2</sub> + 2H<sub>2</sub>O
In this equation, methane (CH<sub>4</sub>) reacts with two molecules of oxygen (2O<sub>2</sub>) to form carbon dioxide (CO<sub>2</sub>) and two molecules of water (2H<sub>2</sub>O).
## HOW IT WORKS
In this model, the atoms in the molecules can be identified through color. Blue represents oxygen molecules, green represents hydrogen molecules, and orange represents carbon molecules. As the heat is increased, the molecules will move faster and faster until they achieve enough energy to react. In this simulation, the molecules all move at the same speed, but in real life each molecule would have its own energy. To represent this, some molecules may start to react sooner than others, but after a certain temperature, all molecules will react.
## HOW TO USE IT
### Setting up
To set up the model, the first thing to do is set the starting amount of methane and the ratio of oxygen to methane by adjusting the appropriate sliders. You may also choose whether or not to include a wall. With the wall on, a grey border will appear around the simulation and molecules will bounce off the wall if they hit it. With the wall off, molecules will loop around if they go beyond the edge of the simulation, appearing on the other side of the model. You may also choose to change the starting energy by adjusting the heat slider prior to starting the model to get a more accurate starting value. When you are ready, hit the “Set Up” button to place the methane and oxygen molecules, calculate initial energy, and set up the wall if necessary.
### Running the model
When you’re ready to start using the model, hit the “Go” button. The molecules will start to move around the simulation, and the graph near the bottom of the interface will start to record the net-energy of the system. You may adjust the heat of the model using the heat slider, and the speed of the molecules will change accordingly.
After a certain temperature the molecules will start reacting. A yellow star is created where a reaction takes place to show the release of energy, and the oxygen and methane molecules will be replaced with molecules of carbon dioxide and water.
If at any time during the model you want to have an easier time finding or identifying molecules, you can chose to hide the products to show only the methane and oxygen molecules. You may also choose to circle molecules to make them easier to identify. The reactants are circled in blue, while products are circled in green.
## THINGS TO NOTICE
While running the model, changing the amount of heat will change not only the speed of the molecules, but also the net-energy of the model.
## THINGS TO TRY
Try using different values for the starting amounts of methane and oxygen. How do different amounts of reactants affect the rate of reaction? Does having or removing the wall change the rate of reactions?
## EXTENDING THE MODEL
In this model, the molecules are all moving at the same speed, and energy from heat is evenly distributed to all molecules. In a real solution however each molecule would be moving at a different speed, and they would transfer the energy from heat by bumping into one another. In a real reaction, heat would come from the container walls. The molecules would take energy from the wall when they hit it, rather than instantly start moving faster.
## NETLOGO FEATURES
In order to make it so the molecules can be circled or set to normal during a reaction, the set-shapes procedure must be run every tick. It checks if circle-molecules? Is true or false, and it asks turtles to change their shapes according to their breed, and sets the default shapes for each breed to make sure new turtles are set to the right shape when they are created.
## RELATED MODELS
The Gas Lab models are good to look into for making molecules behave realistically; some models have the molecules bouncing off of walls and each other with fairly accurate results.
## CREDITS AND REFERENCES
Temperature and the Velocity of Air Molecules (N.D.) Retrieved November 16, 2012 from http://www2.ignatius.edu/faculty/decarlo/surfacepower/pages/KineticTheoryOfGases.htm
Brown, T. L., LeMay, H. E., Bursten, B. E., Murphy, C. J., & Woodward, P. M. (2012). Chemistry, the Central Science. (12th Ed.). Glenview, IL: Pearson Prentice Hall.
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