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What exactly is fire?

  1. Jul 12, 2014 #1
    When we supply energy (activation energy) to a flammable gas, like methane, it burns. A chemical reaction occurs in which atoms rearrange, bonds made and broken. And energy is released. In the form of heat and light. But what is fire, actually? This may be a stupid question, but is this some sort of source of the photons of light? Like, the burning gas's electrons rearranging to give out EM waves in the area of the 'fire'? Light energy doesn't emanate from a filament lamp in the form of 'fire', does it?
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  3. Jul 12, 2014 #2


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    I'm not sure exactly what you want. "Fire" consists of a number of things. There is, of course, the heat which is part of the "energy released" and any time there is energy released, yes, some of it bound to go into electrons jumping from one energy level to the other in the atoms which is then released as light. There will also be the heated gas that has been released from the fuel and "ash", the solids released.

    Light energy from a filament lamp is not "fire". It is the release of energy, yes, mostly light, a little heat. But there is no oxygen taken out of the air so no CO2 released as there would be in "fire" so no heated gas and the filament is not "burnt" so there is no solid "ash"ii.
  4. Jul 12, 2014 #3
    So fire is a physical form of what? Is it the light energy that we can 'see'? Concentrated area of photons? And what do we make of it when fire flickers in wind?
  5. Jul 12, 2014 #4


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    It sounds like you're specifically asking about flames - the area of light that can be made to flicker. This is basically visible light radiated by hot gases as they expand away from the chemical reaction, commonly referred to as burning. The color of the flame varies based on the temperature of the gases as they leave the reaction and cool down.
  6. Jul 12, 2014 #5

    Hmm, so it is the mass of gas that is emitting light seen as flames? Thank you both for your replies. But then it sort of returns to its place after flickering. Maybe that's because when it flickers the mass of gas has done reacting and new mass takes its place, and we don't see the gases leaving in the process when it has been moved aside by flickering?
  7. Jul 12, 2014 #6


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    .... and on the composition of what is burning. Different chemicals / minerals burn with different colour flames

  8. Jul 12, 2014 #7
    So like in a bunsen flame, while we are burning barium, it uses the heat energy of the bunsen flame and reacts with oxygen, producing a flame of its own, coloured green? I guess that is the colour. So what is in that green flame? Barium oxide?
  9. Jul 13, 2014 #8


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    Yes. The gases are emitting visible light as well as a lot of infra-red that we feel as heat.

    Flickering often refers to a candle flame (glowing gas) that's being disturbed as by wind. If you're thinking instead of a campfire or some other larger combustion that creates a "dance" of ever-changing flames, it's the hot gases creating the wind-like disturbances by themselves due to temperature fluctuations as new hot gas from different locations expands from the reaction and cools.

    We don't see the gases as "flames" once they stop emitting visible light as they cool. They cool as they get farther from the reaction, if that's what you mean by "moved aside". And, yes, more hot gas is being created that takes the place in the area(s) of the visible flame.
  10. Jul 13, 2014 #9
  11. Jul 13, 2014 #10
    Not sure, i guess it will be either the heated barium or the heated barium oxide that emits photons in the green wavelength because barium and barium oxide are silvery/white in normal temperatures.
  12. Jul 13, 2014 #11

    Hmm. Thank you all. I think I get it. And yes, I should've Wikipediad it first. =D But it was also the behaviour of flames in which I was interested, and I think I get it now.
  13. Jul 13, 2014 #12


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    You will learn a great deal about flames from Michael Faraday's "The Chemical History of a Candle":

    You will also learn something about science and observation, as well as how to tell an interesting story!
  14. Jul 13, 2014 #13
    I surely will give it a read! =D
  15. Jul 13, 2014 #14
    Fire is actually plasma made out of combustion of substance.
  16. Jul 13, 2014 #15

    Vanadium 50

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    Please read the above messages.
  17. Jul 13, 2014 #16
    does my answer is wrong or i am giving misleading information.
  18. Jul 13, 2014 #17
    Is it atoms which emit light in fire, or do burning reactions form molecules, radicals or ions in excited states which possess induced dipole transitions at light wavelength range?
  19. Jul 13, 2014 #18
    Its hot matter that emits photons but not hot enough to be in plasma state.
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