Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What exactly is fire?

  1. May 29, 2004 #1

    Kerrie

    User Avatar
    Staff Emeritus
    Gold Member

    Is fire considered more energy then element? Never took much chemistry courses in school/college, however I have always wondered what fire is.
     
  2. jcsd
  3. May 29, 2004 #2

    AKG

    User Avatar
    Science Advisor
    Homework Helper

    You can find a quick and easy answer yourself at dictionary.com. Look up "fire" and "flame," and I think that would cover it. I didn't bother to post it here, because there seem to be a few definitions worth considering.
     
  4. May 30, 2004 #3
    I remember wondering about this very question a couple of years ago..

    I THINK this is correct...It's been awhile. Anyway, I think fire is simply the burning fuel. It's so hot that the electrons in the carbons are jumping up to an excited state and then coming right back down, releasing light in the process. THis light is yellow and is (IIRC) due to carbon. Okay, found my book now....Yes, I was partly right...okay:

    The yellow, outermost part, is due to the hydrocarbons (fuel) reacting with the air. The combustion is not 100% efficient and so there is some carbon dangling around, this carbon is heated to incandesence and gives off the yellow color. Try placing this part of the flame over a piece of glass and observe the soot, this is the same carbon that's responsible for the yellow color of the flame. If you could take this soot and heat it up, it would glow yellow. I'm speculating on the last two sentences here but I think I'm correct...

    Next we have the inner cone, which is a bit darker. This is due to unburned fuel which is making its way upwards to react with the air. You can actually try collecting the gas this way, my textbook states, by placing a tube (glass!) into this region and try igniting the other end of it. It takes patience but does work!

    Surrounding the yellow outer flamer is a thin blue mantle, this is where there is sufficient oxygen to allow a complete combustion of the carbon. This is the hottest part of the flame.

    And that does it! Certainly answered my question a couple of years ago and probably finally made it concrete now!

    BTW, nice quote.. I was using the same one for awhile. Brain Damage/Eclipse has been my favorite pink floyd song for as long as I can remember. It's so powerful!
     
    Last edited: May 30, 2004
  5. May 30, 2004 #4

    Les Sleeth

    User Avatar
    Gold Member

    Thanks for asking that question Kerrie, I have always wondered about the mechanics of flame myself. I thought Thunderfvck did a nice job of explaining it too.
     
  6. May 30, 2004 #5

    loseyourname

    User Avatar
    Staff Emeritus
    Gold Member

    Just one thing to add, although this is really pretty obvious anyway. The fuel needn't be a hydrocarbon. Any compound that has hydrogen and carbon in it, or even simple elemental hydrogen, will combust when exposed to oxygen and enough energy.

    Do you happen to know what the flame looks like when pure hydrogen is burned? I can't remember whether or not I've ever seen that, although I probably have.
     
  7. May 30, 2004 #6

    Monique

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Um.. could it look like the sun? :) Incandescent would be the right word, a glowing gas, or for the sun a glowing plasma. As thunderfvck said, it is electrons being excited by the energy released during the violent reaction with oxygen or fusion in the sun. This energy can then be converted into motion = heat or photons = light.
     
  8. May 30, 2004 #7

    loseyourname

    User Avatar
    Staff Emeritus
    Gold Member

    I know what causes the light to be emitted. Would the spectrum of a combustion reaction really be the same as that of a fusion reaction? Considering the fusion taking place in the sun involves only nuclei (which is what plasma is), I don't see how the light emitted would be the same as the light emitted when an electron drops a level or two within a hydrogen atom.
     
  9. May 30, 2004 #8

    Monique

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    A plasma is an ionized gas. The spectrum would depend on the difference in energy between the excited and ground state of the electron. Also the ability to loose the energy in other ways (or the inability to do so for phosphorescent compounds).

    I'm not really sure how different the spectrum of hydrogen fusion or hydrogen oxydation would look, you're right it could be very different.
     
  10. May 30, 2004 #9
    My book again comes to the rescue!

    It burns with a blue flame.

    "a controlled flow of hydrogen will burn steadily in air or oxygen with an almost invisible, intensely hot, blue flame"

    I wish I could have seen Hindenburg blow! :approve:
     
  11. May 31, 2004 #10
    The color of the flame depends on various factors, such as temp., fuel/oxygen mix, etc. Hydrogen can burn blue, yellow, or simply explode sans fireball.
     
  12. May 31, 2004 #11

    Kerrie

    User Avatar
    Staff Emeritus
    Gold Member

    so fire is considered pure energy? and that energy is a direct reaction of different elements mixing with one another? although i never had an official college course in chemistry, i remember going to an education summer camp and learning in a brief amount of time a little bit about the table of elements (which i found interesting :shy: )
     
  13. May 31, 2004 #12
    Yeah, I'd say that fire is a whole lot of heat energy.
     
  14. Jun 2, 2004 #13
    The flame that you actually see is just superheated gas. It's like when you heat a stovetop and it begins to glow red, the gas heats up and glows itself. There's also light being emitted by the chemical reactions themselves. There's quite a bit of stuff going on in a single flame. It's not really plasma, if I remember correctly, because the nuclei aren't stripped completely bare of their electrons, but there's plenty of ions in there.
     
  15. Jun 2, 2004 #14

    Monique

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    No, it is not considered pure energy, but a lot of energy is released in heat and light.
     
  16. Jun 2, 2004 #15

    loseyourname

    User Avatar
    Staff Emeritus
    Gold Member

    Well, the fire you see is pure energy. The only thing anybody sees is light energy; that is all the photoreceptor cells in our retinae are equipped to detect.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: What exactly is fire?
  1. What is fire? (Replies: 3)

  2. Fire ! (Replies: 1)

Loading...