Kristi Jean Gourd, age 10, of des Moines, Ian. For her question:
Where does wood go when it burns?
A flicker campfire gives and takes. It gives warmth and flaming tongues of light, which pierce the darkness. It takes a pile of bone dry logs and perhaps a wad or two of paper. When the give and take is finished, the fire is cold and dead and the wood has disappeared, leaving no more than a small pile of charred ashes.
A boning log fire is very busy and a lot of different things are going on at the same time. We see the flickering flames of light and we feel the heat pouring forth from the blazing wood. But we cannot See or feel the most important events that axe happening. These are chemical events, and fire itself is a chemical event.
Fire is called a chemical change. When a log of wood burns to ashes, its chemicals axe changed to different chemicals. This is the basic event of the burning. Heat and light Just happen to be given off as wood is changed into different chemicals.
Chemicals are made of molecules, and molecules are bundles of assorted atoms. Wood is made mostly from molecules of cellulose, plus a few molecules of gummy resins and tough cements. Each molecule Of cellulose is a wad of carbon atoms, hydrogen atoms and atoms of oxygen. The miniature bundle is knotted together with energy.
When the temperature gets hot enough, the atoms in the cellulose molecules break apart and go their separate ways. They use energy from the heat to out pull the energy that binds them together. The molecules of woody cellulose are very different from their separate atoms. Carbon is a sooty substance of hydrogen and oxygen are invisible gasses.
As the burning chemicals change, they use oxygen from the air. Some of the freed carbon atoms team up with atoms of oxygen to make molecules of carbon dioxide.
Atoms of hydrogen and oxygen combine to form molecules of water vapor. Fragments of carbon Stream up in clouds of sooty smoke. The chemicals in the wood change into invisible gasses and fly off into the air. The wood seems to disappear.
A log of wood will start to burn when it is hot enough to reach its kindling point. A wad of paper has a lower kindling point and needs less heat in order to start burning. We use wads of burning paper to bring the wood up to its kindling point. When the wood catches fire, the bursting molecules give off heat and the burning keeps itself going. It stops when there are no more woody chemicals to be changed into invisible gasses.