Let's Make a Fire!
This activity models the burning of various fuels (coal, natural gas, and hydrogen gas), using styrofoam spheres of various sizes and colors to represent the atoms involved. Concepts illustrated include:
- fires need oxygen as well as a fuel
- in a chemical reaction, atoms don't disappear, or appear out of nowhere, or change into different kinds of atoms
- how chemical notation provides "accounting" for atoms in a reaction, and in a molecule
- burning produces "waste products" ("exhaust fumes") - most commonly CO2 and H2O
- burning releases energy that was stored in the fuel (as chemical energy), converting it into light and heat
- (optional, for higher grade levels) atoms bond together in several ways - e.g. single and double bonds
- (optional, for Web page record of activity) digital camera - take pictures of atoms and molecules at all stages of activity
Materials
For each participating student, or group of students:
- paper and pen (or pencil) - recording is important!
- 1 C (large black styrofoam ball)
- 4 H's (small blue styrofoam balls)
- 4 O's (large white styrofoam balls)
- 4 toothpicks and 4 toothpick-sized pipecleaner segments for atomic bonds; replace the pipecleaners with 2 more toothpicks if double bonding not represented
- (optional) digital camera to record and webify the activity
Procedure
Form groups, distribute materials, and explain the process of making molecules (at a grade-appropriate level - e.g. double bonds and tetrahedral molecules are advanced concepts, optional for lower grades). For more details, refer to these handy tips and assembly instructions).
Have each group assemble from their atoms and bonds 2 H2 and 3 O2 molecules (double bonds for more advanced classes). They should write a description of their procedure, including an inventory of materials used, and drawings of the molecules produced (see pictures). Have them relate the picture and model to the chemical formula
Start with the simplest combustion - C + O2 -> CO2; have the students "act it out" with the C and one O2 molecule. They should record in writing the chemical equation, and ponder its connection to the manipulation of the models; drawing also good.
Next, "burn" the 2 H2 molecules with the remaining O2 molecule, to produce 2 water molecules; record as above. Shape of H2O should be described grade-appropriately (ranging from "like Mickey Mouse" to "tetrahedral bonding").
Now assemble one CH4 and 2 O2 molecules to match the pictures. Using the experiences above, enact and write out a chemical equation for the combustion of methane. In Nature, and particularly in estuaries, methane (also known as "swamp gas") is produced and can burn spontaneously.
A very important form of "burning fuel" is necessary for all living things. Respiration uses food as fuel (e.g. sugar), and oxygen (inhaled by lungs or gills) to burn it, releasing energy.