How and Why Things Burn: Teacher's Notes

Activity: Thinking About Combustion

Safety: First and Foremost

• If you choose to illustrate any of the principles shown on the webpages as demonstrations or as hands-on activities, it's essential to follow all safety precautions to the utmost. Students may need to be reminded that burns are painful and can be disfiguring, and trying these types of experiments can be very dangerous. It is our hope that in providing video footage the students will be able to see the chemistry and learn from it without any risk whatsoever.

• Wear safety goggles at all times.
• Provide a safety shield for protection of the students and of you.
• Perform all experiments and demonstrations in a well-ventilated area, in open, still air. (That is, if you do this outdoors, a breezy day can be unpredictable and hazardous.)
• Never ignite anything in a sealed or closed container.

Objectives

• To understand the key components in how things burn; specifically the combustion triangle.
• To understand the stages of the combustion process.
• To understand the role of thermodynamics and kinetics in the combustion process

National Science Education Standards: Content Standards

This activity fulfills the following within the Content Standards: 9-12

• Content Standard A: Science as Inquiry
  Safety must be an integral component of their investigations.
• Content Standard B: Physical Science
  • Structure and Properties of Matter
    
  • Chemical Reactions
    

Materials

• There are no materials required. This activity involves reading and understanding the content presented on the student pages.

Method

• Have the students carefully read the content pages.

Questions

1. Water is often used to put out a fire. Using the combustion triangle, why should this work?
2. You're frying catfish in a pan on the stove and turn your back for just a moment The fish and oil in the pan catches fire. Will placing the lid on the pan put the fire out? Explain using the combustion triangle.
3. Explain the molecular scale changes (or stages) that take place when your pan of catfish catches fire.
4. Explain the macro scale changes (or stages) that you would observe when your pan of catfish catches fire.
5. It has been stated that wood going to the combustion products of carbon dioxide and water is thermodynamically favorable. What does this mean? Why is this true?
6. If wood going to the combustion products of carbon dioxide and water is thermodynamically favorable, why doesn't wood spontaneously catch fire?

Extensions

1. Have the students think about the processes when a volatile liquid like gasoline burns.
2. Can you boil water in a paper cup over an open flame? Why or why not?
   NOTE: You can do this extension as a demonstration or the students can do it.
3. Magnesium metal will burn in carbon dioxide (dry ice). How is this possible? (Have the students revisit the fire triangle.) The students can view a video of this demonstration at:
   Mg burning in dry ice where it continues to burn.