# Where does fire go?

1. Jul 12, 2005

### killza

when u have a fire on a candle, and u blow the fire out, where does it go? does it evaporate into thin air? or does it just disappear? can fire really evaporate? i been wondering about this question ever since my math/science teacher brought it up

2. Jul 12, 2005

### PatPwnt

The fire itself is the reaction taking place when the wax of a candle burns up the wick. I guess you could say the fire turned into smoke.

3. Jul 12, 2005

### Integral

Staff Emeritus
"Fire" is simply iridescent chemical vapors. As long as the temperature is sufficiently high the vapors will glow, as soon as the temperature falls below some critical point the vapors will still be there but will not glow. Since the glowing vapors are a product of the chemical reaction occurring in the fuel, when the reaction halts so will production of the vapors. Thus snuffing the flame eliminates both the source of the vapors and the energy required to create a glow in the vapors.

4. Jul 12, 2005

### tony873004

On a related note, what's the difference between something on fire and something smoldering?

If a log is in a campfire, it can either burn (fire) to ash, or smolder to ash. But it seems like fire is more than just heavy-duty smoldering. When the breeze blows, sometimes smoldering things catch fire. And often there's a sound associated with this.

Also, when you blow out a candle, sometimes the wick continues to smolder for a few seconds.

Does smoldering require oxygen like fire? I guess I could test this myself

5. Jul 12, 2005

### Integral

Staff Emeritus
I believe that smoldering means that the reaction is progressing slowing, not producing enough heat to create flames. Addition of $O_2$ could change that.

6. Jul 12, 2005

### brewnog

I would call hot, glowing combusting gases 'flames', and hot glowing combusting solid carbonny stuff 'embers'.

Yeah, it's still hot. Being solid, it takes longer to cool down than the gases, which are quickly cooled and dissipated.

You certainly need oxygen to have a fire. If you have no fire, you have no heat, and therefore you have nothing to make the embers glow. However, if you remove oxygen from a fire, the embers will continue to glow, but will cool down until they stop glowing.

The glowing isn't a direct result of fire, it's a result of heat.

Bear in mind that heating stuff up without oxygen will often also cause it to glow. The difference is that with no oxygen, no combustion is occuring, it's just hot and glowing. Fire requires oxgyen, since it's combustion. This happens to produce heat, which is why everything glows.