Was fire unsubstantial without oxygen?

[Jerryt12]

If so, why?

[Sisyphus]

I don't know what you mean by unsubstantial, but there's no such thing as fire without oxygen. That's what fire is: something rapidly combining with oxygen.

[Mr Skeptic]

You can use other oxidizers instead of oxygen. However normally oxygen is the oxidizer since it is so abundant in the air.

[insane_alien]

i'd hardly call a hydrogen - Fluorine reaction unsubstantial

[D H]

Hey everyone! Before answering, think a bit: Does this look like someone fishing for help with homework without say that this *is* homework?

[Jerryt12]

thanks for all the replies, but what I don't understand was why was oxygen needed in order to start a fire? (sorry, I should be more specific.)

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From Mr. Skeptic, I can conclude that it's because oxygen is a type of oxidizers. But doesn't oxidizers help releases electrons from others substances? How does that helps make a fire?

[Mr Skeptic]

The way it works is that (almost always) forming chemical bonds releases energy. Forming stronger bonds releases more energy than forming weaker bonds, and also trading a weak bond for a strong bond releases energy.

 

The rules governing what makes a strong and weak bond are rather complicated, but in general if you combine a highly electronegative atom (an oxidizer; one toward the top left of the periodic table) with a significantly less electronegative atom (almost all of them) then you get a fairly strong bond. Oxygen is actually the second most electronegative atom (beat only by fluorine) and is highly abundant, making up 21% of our atmosphere.

 

As you might know, heat usually speeds up chemical reactions (more particle collisions and they are more likely to overcome the activation energy). Burning is a chemical reaction that releases heat, and in a sense is therefore self-catalyzing. That is why paper doesn't burst into flames in the atmosphere but will burn nicely once you put a lit match to it.

 

Burning does not require a flame. A flame will occur if there are volatile constituents, such as hydrocarbons.

[Jerryt12]

thank you.

 

Just to make sure.

 

it's the forming of strong bonds that releases energy in term of flame.

 

So when carbon reacts with a low electronegative element, a fire is created?

[Mr Skeptic]

No, the flame is not due to the carbon but due to the volatiles contained. If you burn coke (coal roasted to remove the volatiles), you will get little or no flame. If you burn hydrogen you will get a flame without involving carbon. The heat produced is the energy that is released by forming more or stronger bonds.

 

Almost all chemical reactions will produce heat, especially ones that happen spontaneously. I'm not sure what the exact requirement is to consider it a fire.

[Jerryt12]

what do you mean by volatiles?

[Mr Skeptic]

Volatiles are substances that evaporate easily. For the purposes of a flame, anything that has a boiling point lower than the temperature of the fire, will evaporate. If it is flammable, it will both evaporate and burn (so form a flame).

[Jerryt12]

So if a bond is formed the energy = heat. But if a bond is form with a substance that is volatile, then a flame will be produced.

[Mr Skeptic]

Pretty much. A volatile substance will vaporize and then it can burn in the gas phase. Compare to embers that are burning in the solid phase (rather at the solid/gas boundary, ie the surface)

[Jerryt12]

I know that the properties of a substance depends on their electron configuration.

 

So how would we know if a substance is volatile by looking at their electron configuration?

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so if we're burning woods, is oxygen the volatile substance that start the fire?

[Mr Skeptic]

Wood contains lots of hydrocarbons (cellulose is essentially a chain of glucose sugars). The heat can get these to react and form something volatile. Wood is largely made of carbon, hydrogen, and oxygen. Some of the carbon can form volatile substances (methane, ethane, alcohols, carbon monoxide, ...) by combining with the hydrogen and oxygen, and some remains as charcoal.

http://en.wikipedia.org/wiki/Pyrolysis#Fire