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Q & A: What is the State of Matter of Flame?

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Most recent answer: 11/17/2013
Q:
What is the state of matter of flame?
- aman (age 17)
Jamshedpur,jharkhand,india
A:

Thanks for the question, Aman

Fire is an oxidizing chemical reaction that releases heat and light. The actual flames that you see moving and glowing when something is burning are simply gas that is still reacting and giving off light. Plasmas are gases in which a good fraction of the molecules are ionized. Ordinary flames ionize enough molecules to be noticeable, but not as many as some of the much hotter things that we usually call plasmas.  (See  for a guide to an experiment that uses the electrical conductivity of a flame caused by its ions.)

Of course, plasma and fire can both radiate visible light, So what's the big difference between an intense plasma and the weakly ionized gas in an ordinary flame? Plasma arc welding () offers a good example of plasma and its qualities in comparison to ordinary flames. In plasma welding, gas is plasmized via an electrical current and in the process heated up to 20,000o Celsius and shot onto a material. The plasma gives off ultra-violet rays which can blind the welder if not protected, and cause tissue damage to bystanders. Can you imagine if candlelight were that strong?

Samson (mods by mw)


(published on 06/25/2012)

Follow-Up #1: quantum fire

Q:
You answered what is fire on a material level, but is there a quantum level? Photons are released through a chemical/heat reaction that breaks down the magnetic force holding together the electrons in the material being burnt and being seen as a flame as they disperse...? Something like that?
- jim w (age 42)
seneca il usa
A:

Sure, it's kind of like you say except that the forces are almost all electrostatic, not magnetic. The new chemical combinations formed have lower energy than the old combinations. The extra energy has to go somewhere. The strongest long-range field that the charged particles (mainly electrons) couple to is electromagnetism, so the energy leaves as electromagnetic waves (photons). The reaction hardly happens until a flame gets going because it takes some energy to first rip apart the old molecules before allowing the new ones to form. The net process releases energy, which keeps it going once it's started.

Mike W.


(published on 11/17/2013)

Follow-up on this answer.