How does coal burn?
Coal, like everything else, is made of molecules. The molecules are bundles of atoms bound together with energy. When it burns, the coal goes through a chemical change. Its molecules break apart. The coal is changed into other substances, most of them invisible The energy that bound the atoms together in molecules goes off as heat. Lets see how the coal molecules were built in the first place. This too, was a chemical change„ It was a cementing job and it used up energy instead of giving off energy. The energy, of course; was sunlight as it fell upon ancient forests. The trees used the sunlight in their magic recipe for making plant food. Some of the food was rebuilt into cellulose, the stuff that makes wood. Cellulose molecules are made of carbon$ hydrogen and oxygen. The plants took these atoms from the air and from moisture. They used the energy of sunlight to tie them up in complicated molecules. Molecules are not packed close together in a solid‑looking log of wood. Actually, they
