Did you know that fire is a chemical reaction? Fire is the most common form of a combustion reaction. Combustion, or burning, describes an interaction of oxygen and a fuel source that results in heat and light, usually in the form of a flame. Combustion combines the fuel source and oxygen to create an exothermic reaction, a reaction that generates heat above and beyond the heat needed to initiate the reaction.
In order to have a combustion reaction, the fuel and oxygen need a catalyst. A catalyst is something that causes or speeds up a chemical reaction without itself being altered. The catalyst for a fire is usually temperature. The fuel has to reach a certain temperature and be in the presence of oxygen before it will ignite. Because fire is an exothermic reaction, a single spark (which can reach temperatures over 2,000 degrees!) is hot enough to begin the combustion process, and the expelled heat is enough to keep the reaction going.
Without all three ingredients – fuel, oxygen, and heat – a combustion reaction is not possible. A fuel source like paper or wood, in the presence of oxygen but without heat, will not ignite all by itself. If it did, trees and papers would be constantly burning! Likewise, having fuel and heat might ignite a reaction, but without oxygen, the reaction cannot be sustained. That is the principle we will examine in this experiment.
The Experiment
Supplies: Baking soda, a shallow bowl, a tea light candle, vinegar, a lighter or match, and an adult helper.
What to do: Sprinkle some baking soda in the bottom of the bowl. Make sure you use enough to create a nice, even layer. Set the tea light in the middle of the bowl. Ask your adult helper to light the candle. Slowly and carefully pour the vinegar into the bowl, making sure not to splash or extinguish the candle as you pour. What happens to the baking soda? What happens to the candle?
What is happening: Combining vinegar and baking soda causes a chemical reaction. One of the products of that reaction is carbon dioxide, which is a heavier gas than the oxygen/nitrogen combination in the air. The carbon dioxide settles at the bottom of the bowl, displacing the oxygen surrounding your candle. Without oxygen, the reaction cannot be sustained and the flame goes out.
Links
For an overview on combustion, check out this article on Britannica Kids.
For more in-depth information, Mocomi examines different types of combustion, flames, and fuels.
To learn more about how fire extinguishers work to put out flames, the journalists at The Conversation answers questions from Curious Kids.