Re: Why does a flame require oxygen

Hi Alex

Well, you’re right to not understand why a flame can only exist if 
oxygen is present, because this is not true. Flames can exist with a 
variety of substances as well as oxygen. It is probably best that i 
explain what a flame is (basically):

First: all the material we use is made up of atoms. These bond 
chemically with one another and form objects. Gases are also made 
up of collections of bonded atoms.

Second: said bonds may be broken if given enough energy.

Third: after being given enough energy, some substances will react 
together and the reaction will give out energy, these are called 
exothermic reactions.

Fourth: energy can manifest various ways, such as sound, light, and 
heat.

So if a reaction between two substances gives out energy, it can 
produce light, and so, in some cases, you can see a flame.
The air is made up of about 70% Nitrogen, 25% Oxygen and 5% 
Noble gases, Carbon Dioxide and Water. Apart from oxygen, these 
compounds are relatively stable, and so most reactions involving air 
use oxygen. I can’t think of any specific examples, but i can promise 
you that there are many reactions which give a flame, or at least light, 
without oxygen. Chlorine is probably a good substitute for oxygen as it 
is a quite powerful oxidising agent and it is gaseous at room 
temperature (btw- don’t breath it in, it’s not very pleasant, honest). I 
think reactions of Sodium + Chlorine and Phosphorus + Chorine 
should give light and, under controlled conditions, a flame. I’m not 
sure what colour phosphorus gives, but sodium should be yellow. 
Even so, don’t try these reactions, they could be lethal. (Violent 
reactions tend to give light, y’see).

I hope this answers your question. I’d like to tell you how to do a 
demonstration of a non-oxygen flame, but i can’t remember any 
examples, sorry!

Paul Henderson

Dan Berger adds:
Such demonstrations aren't normally done for a very good reason: non-oxygen 
gases that will support combustion are quite dangerous. You should be able to 
find videos of such demos on CD-ROM collections such as "Chemistry comes 
alive!" published by the Journal of Chemical Education.

Many substances will spontaneously combust in an atmosphere of fluorine, but 
fluorine is even more dangerous than chlorine! As a matter of fact, OXYGEN is 
a horribly corrosive and dangerous gas, except that our metabolisms have 
learned to deal with it...