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Name:  Zach
Status: student
Grade: 4-5
Location:CA
Country: N/A
Date: 1/24/2005


Question:
Why does fire need oxygen to burn?


Replies:
"Burn" is really a term used to describe a chemical reaction known as "combustion". A combustion process usually requires oxygen or some oxidizer. Thus, when we say we burn something, what we are really doing is allowing the combination of that substance with oxygen. This process usually means that a lot of energy is produced. The energy is usually released in the form of heat and light. This heat and light we call "fire". thus, it is not so much that fire require oxygen, but rather that the process of combining oxygen with a substance (in a combustion process) produces heat and light (fire).

Greg (Roberto Gregorius)


Well, Zach, fire is not a "thing", not a substance. It's an event, a "happening", like a tall pile of building-blocks falling down, or a balloon popping. My pile of bricks need height and gravity to have an avalanche. Fuel needs oxygen to have a fire.

Fire is two different substances that really like each other, in the act of "falling together" as fast as they can. Water is a very stable substance made of two hydrogen atoms and oxygen atoms, strongly stuck together. If you pull them apart and put all the hydrogens in one place and all the oxygens in another, Then they could have a fire if they are allowed to get back together again.

Other kinds of atoms can have a fire, too. Lithium metal plus fluorine gas make an abnormally strong fire. Fortunately there is not much of either one around here.

Most fires we think about are carbon and hydrogen atoms re-joining with oxygen atoms, to make the very stable substances carbon dioxide gas (CO2) and water (H2O). Most burnable substances are made of carbon and hydrogen, and the air is where the oxygens are always waiting around.

This is a dangerous situation, a little like putting all your heaviest boxes on the highest shelf. Who built this dangerous situation? Plants! All the green plants in the world are constantly using sunlight to pry apart old CO2 gas. They keep the carbon to build themselves, and release the oxygen into earth's atmosphere. You cannot quite blame them for growing, and they have certainly helped us to exist.

I guess the original CO2 gas came out of the earth's crust through volcanos.

So fire is a quick release of same chemical energy that keeps us living, but it is released too fast, without a living thing carefully and slowly using the energy.

Jim Swenson



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