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Fire

Fire doesn't destroy the matter in wood—it just changes it.

All the atoms that are present at the start of a chemical reaction still exist at the end. So why is the pile of ash remaining after a log burns so much smaller than the log?

Energy is released when the atoms in cellulose and oxygen molecules are rearranged to form water and carbon dioxide.

Wood is made largely of carbon, hydrogen and oxygen atoms joined together to form cellulose molecules. When the cellulose burns (in oxygen) the bonds holding these atoms together break. New bonds are formed. Hydrogen (H) joins with oxygen (O) to form water (H2O). Carbon (C) also joins with oxygen (O) to form carbon dioxide (Co2).

The carbon dioxide and water molecules are invisible gases (the water is present as steam). All we see is the pile of ash containing the bits of wood that didn't burn completely.


Burning wood
magnifyBurning wood


Combustion reaction
magnifyCombustion reaction
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