John Esh, age 11, of Strasburg, Pa., for his question:
WHAT EXACTLY IS FIRE?
Certainly it is not animal, mineral or vegetable. It's even hard to say whether it is alive or dead. In the past, many great brains, puzzled by the nature of fire, came up with some fanciful ideas to explain it. Modern scientists tell us that fire is a chemical reaction something that happens on the level of mini molecules.
We are told that the world is made of invisibly small atoms and molecules. This is true of all gases, liquids and solids. But there is something else to this oversimplified statement, something that keeps the world of assorted molecules in constant agitation. This is energy, which performs numerous invisible activities. Molecules, as we know, are packages of atoms bound together by various chemical energies.
The world of nature constantly changes because multitudes of molecules break apart and their atoms reassemble to form molecules of other substances. These modeling and remodeling jobs are called chemical reactions. And all of them involve molecules of matter plus energy.
Some chemical activities take outside energy and use it to build separate atoms into molecules. For example, plant photosynthesis uses energy from sunlight to build sugar molecules from atoms of carbon and hydrogen. This borrowed solar energy is used to hold hydrocarbon molecules together. Plants use them to build molecules of woody cellulose, which may be changed to coal and survive through millions of years.
Other chemical activities release energy as molecules break apart. This happens during the burning process, which uses oxygen from the air to break up molecules of fuel. For example, the fuel may be coal. Its molecules, remember, are tied together with solar energy borrowed long ages ago.
In a blazing coal fire, the chemical reaction uses oxygen to untie the hydrocarbon molecules created long ago in some ancient forest. This frees atoms in the molecule packages to go their separate ways.It also releases the molecular energy that bound them together ¬which goes off in the form of heat and creates the blazing flames.
The chemical reaction which causes fire is called combustion. It may be fast and blazing bright, as in a campfire. Or it may be the slow burning process used by living cells to process foods and create their own warmth and energy.