What is fire?

[Teatowel]

I mean, what exactly is it?

I thought that fire was just the heat and light given out by a chemical reaction, eg magnesium burning in oxygen, or paper burning in oxygen. Would it be wrong to class fire in a solid/liquid/gas/plasma system?

 

[crypticlogin]

What we see as fire is the visible spectra of the energy-releasing chemical reaction of whatever is burning. Unless there was a new classification since I took HS chemistry, energy isn't classified as a liquid, solid, gas, or a plasma. I always wondered about this myself for a few years back...

 

[Elledan]

Fire: a certain substance is heated sufficiently to vaporize the substance. A thin layer forms above the substance where ever heat is applied. This layer of vaporized particles (gaseous state) then mixes with another substance, usually oxygen. During this chemical reaction energy is released in the form of radiation.

Fire itself consists out of a multitude of chemical reactions, during which all involved substances are in a particular state (being gaseous, solid or liquid). For this reason one can not define fire as being 'gaseous', 'liquid' or anything else. Such a definition is only possible for the involved substances.

BTW, basically, 'fire' is what we call a very rapid oxidation. E.g., the rusting (oxidation) of iron is chemically identical to a fire, yet we don't call it that way

 

[Zach]

And if a fire is burning cleaner there is less flame, signifiying that fewer particles (or vapors of matter, whatever) are escaping the reacton.

 

[RSMemphis]

Okay, here is what happens.
The material that burns oxidizes exothermically (giving of heat). The gases that emerge from the material are really hot, and therefore mostly ionized.
Thus, it's a gas and a plasma, but the fact that it's a plasma is not relevant. From the color of the flame you can tell the temp of the emerging gas, red is cold (<4000 K), yellow is warmish (5000 - 5500 K), blue is hot (8000 K)

 

[Demon-Xanth]

Fire is actually matter in the 4th state: Plasma. Plasma is essentially a highly charged gas.

 

[RSMemphis]

<< Fire is actually matter in the 4th state: Plasma. Plasma is essentially a highly charged gas. >>



Mmm... Free electrons. Shiny!

I am not sure I would call Plasma a 4th state. It's still a gas, just a completely ionized gas. Has different properties though (as in conductivity and nice things like that).

Anyway...

 

[Demon-Xanth]

Scientifically speaking, plasma is often regarded as a state of matter.

 

[RossGr]

I once read of how to make a flame speaker, Two platinium needles positioned in a flame and connected to a sound source. I suppose that you could use any type of needles but steel would not last long in the harsh invironment of the flame. This is supposed to form nearly a perfect speaker, though I cannot see how it would make good a woofer !

 

[LordMagnusKain]

i think that fire is the sperit of the sun, consuming what it feals is not as pure as the sun himself.

 

[CTho9305]

<< i think that fire is the sperit of the sun, consuming what it feals is not as pure as the sun himself. >>

 

[Shalmanese]

Fire is not plasma becuase a condition for plasma is that ALL electrons are stripped from the atom. AFAIK, fire only has enough energy to strpi the outer shells most of the time. Also, The colour from fire could be from 2 different things. First, certain metal ions have electron shell energy differences within the visible spectrum which means, if excited, it will emit a very pure spectral colour from the electron descending down a shell. Second, is due to temperature from balckbody radiation and this is emitted in a continuous spectrum depending on temperature.

 

[Jerboy]

<<
BTW, basically, 'fire' is what we call a very rapid oxidation. E.g., the rusting (oxidation) of iron is chemically identical to a fire, yet we don't call it that way >>



Many finely divided metal will burn in presence of strong electronegative gas(especially Cl and F) without oxygen. I haven't tried it myself, but seen it in a chemistry text book.

The reaction mits light and producing heat. I think this can be considered fire.

 

[RSMemphis]

Oxidation does not necessarily involve oxygen.
Oxidation means that a material gives up an electron (and that oxygen or whatever else is involved accepts it)
Reduction means that the material receives an electron.

It's called oxidation because oxygen is quite often involved in the process.

 

[RSMemphis]

<< Fire is not plasma becuase a condition for plasma is that ALL electrons are stripped from the atom. AFAIK, fire only has enough energy to strpi the outer shells most of the time. >>



Definition: A highly ionised gas in which the number of free electrons is approximately equal to the number of positive ions. Sometimes described as the fourth state of matter, plasmas occur in interstellar space, in the atmospheres of stars (including the sun), in discharge tubes, and in experimental thermonuclear reactors.

Because the particles of a plasma are charged, its behaviour differs in some respects from that of a gas. Plasmas can be created in the laboratory by heating a low-pressure gas until the mean kinetic energy of the gas particles is comparable to the ionisation potential of the gas atoms or molecules. At very high temperatures, from about 50 000 K upwards, collisions between gas particles cause cascading ionisation of the gas. However, in some cases, such as a fluorescent lamp, the temperature remains quite low as the plasma particles are continually colliding with the walls of the container, causing cooling and recombination. In such cases ionisation is only partial and requires a large energy input. In thermonuclear reactors, an enormous plasma temperature is maintained by confining the plasma away from the container walls using electromagnetic fields.

Thus, complete ionisation is not a requirement. In fact, only one electron needs to be removed from every atom for it to be a plasma, and there is enough energy for that.



<< Also, The colour from fire could be from 2 different things. First, certain metal ions have electron shell energy differences within the visible spectrum which means, if excited, it will emit a very pure spectral colour from the electron descending down a shell. Second, is due to temperature from balckbody radiation and this is emitted in a continuous spectrum depending on temperature. >>


Actually, if you look at the spectrum of a fire, you will see a blackbody distribution with the material absorption lines of whatever is in the gas.

 

[PuterGuy]

Flame is classified as a plasma which is the fourth state of matter. RSMemphis is absolutly right by saying that all the electrons do not need to be removed from the atom. actually an atom is not an atom without any electrons, the atom would fall appart because all that would be left is the positive protons and the neutral neutrons. Shalmanese is wrong by saying that. also the new theory on electrons is that there are no more shells of electrons. Electrons are now beleived to move in a "cloud" around the neucleus of the atom. Personally i am not sure if flame really consists of atoms. I think that there are some parts of flame that science does not know about yet. Other substances maybe, or flame might not even be made of atoms at all, there could be other types of particles that make up flame. Until there is a way to trap and preform sucessful experiments on fire these questions cannot be answered accuratly. Everything is theory as of now.