Dolly Garrison, age 10, of Richmond, Virginia, for her question:
What is fire?
Fire is not an animal, a vegetable, or a mineral. The proper name for it is a chemical reaction. This means that some kind of action goes on between a number of chemicals, Since just about everything can be called a chemical this is not hard to believe. For the fact that there is action speaks for itself. In a log fire, we can watch a lump of wood change into a handful of ashes. A change of this kind is quite a dramatic chemical reaction.
A chemical reaction may be of two kinds. One uses up energy. The other releases energy. The log of wood was created by a chemical reaction of the first kind. The energy used was sunlight. Through countless sunny days, the green leaves of the tree worked to make plant food. They used water from the soil and gases from the air and bound them together in a secret recipe using sunlight. The sunlight was the energy used to make molecules of plant food.
Some of these molecules went through several more chemical processes and finally became cellulose. This is the tough substance a tree needs to build the cell walls which make its trunk and strong branches. These chemical processes are the kind that use energy to build.
A log of wood is made mostly of cellulose molecules, along with some resins and cements. Let's throw it into a blazing fire. The heat of the fire agitates the various atoms and molecules in the wood. They are soon tearing around at great speeds. The molecules break up into atoms which fly off on' their own. The molecules of cellulose are no more.
The liberated atoms, however, do not cease to exist. Some of the carbon atoms fly off and join with oxygen atoms in the air. Together, the two gases form carbon dioxide. Some of the hydrogen and oxygen atoms go off as water vapor. A good deal of the carbon goes off as smoke and soot.
The heat and flames of a fire are forms of energy, The energy from sunlight was used to tie atoms into the bundles we call molecules. The fire untied these bundles and energy was freed as heat,, The flames were burning gases.
The chemical reaction of burning is not always as dramatic as a blazing fire. Our bodies use our food by a slow burning process. This too is a chemical reaction which releases energy. The burning process may be slow or fast, but it always needs oxygen. And in the process it always gives off some kind of energy.