The middle of January is often the coldest time of the year in most of the United States. Fireplaces blaze in the evenings, and children look wistfully at the burning logs or at glowing candles and ask, "What makes the fire?" Their parents' response is usually, "Uh, hmmm, let's see, uh. . . ."
Yes, well, today let's see.The phenomenon we call fire or burning or combustion involves a chemical reaction, and chemistry is not something that most parents feel comfortable about discussing with their children. And that's fine, because what I call "family learning" does not mean "classroom learning at home," nor is the learning reserved for children alone.
In fact, it is the attitude of the parents, far more than their schooling or their knowledge, that determines whether family learning will become a part of the family life in any particular home.
In highly technical areas, such as chemistry, parents should concentrate on getting the very basic facts out in the open (the terminology, for example), and then providing encouragement for their children to inquire and to investigate how those facts can help them to better understand some of the things they see in the world around them.
The wonders of a candle flame and the apparent disappearance of the wax can be explained by telling children that the wax (or paraffin or tallow) is a mixture of substances called hydrocarbons - that is, molecules that contain atoms of hydrogen and carbon. Now when these large molecules are heated, their hydrogen atoms and their carbon atoms get excited and begin to move about rapidly, crashing into other atoms nearby. When oxygen atoms happen to be nearby (oxygen makes up about a fifth of the air we breathe, most of the rest being nitrogen), the carbon atoms and the hydrogen atoms link up with these oxygen atoms to form completely new and different molecules. A single carbon atom can join with two oxygen atoms to form carbon dioxide (CO 2 ).
Two hydrogen atoms can join with a single oxygen atom to form water H 2 O). But in the process of breaking down the large hydrocarbon molecules into smaller molecules like carbon dioxide and water, energy is given off in the form of heat and light. The yellow flame is actually just millions of hot carbon atoms that didn't link up with any oxygen atoms. These atoms glow (just like a piece of burning coal, which is also carbon) and then cool to form the black particles in soot and smoke.
You can't see the carbon dioxide or the water that the burning candle or paper or logs have changed into because they are sent into the air as gasses and vapors. But if you hold a clean drinking glass above the burning candle, you can see the water vapor condense into droplets on the inside of the glass.
The candle wax itself won't burn very readily, and so a cotton wick is used to heat the wax into a liquid, which is then pulled up the wick by a process called "capillary action." This process, which is the same way that trees pull ground water up through their trunks, can be demonstrated by touching the corner of a paper towel to a puddle of water on the counter top.
But even liquid wax will not readily burn, and so the flaming wick turns it into a gas. You can show your children that it is the gas, not the wick or the solid wax, that produces flame by blowing out the candle and then quickly holding a lighted match an inch ABOVE the wick. Presto! The vaporized wax that has risen above the wick relights immediately, starting the entire chemical reaction all over again.