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I had this question from the day(9 years old, now 16) that i learned about states of matter. I have asked so many of my teachers some of them told me gas some as plasma etc. can anyone answer my question? Recently I've learnt that plasma state is obtained when all the electrons from the atom are removed. Obviously its present in sun due to high temperature.

Akshay Nagraj
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  • This is cross posted on Chemistry.SE http://chemistry.stackexchange.com/questions/7933/to-which-state-of-matter-does-the-flame-belong-to –  Jan 21 '14 at 10:25
  • All the electrons don't need to be removed from an atom to be considered plasma. Just removing one electon from each atom is sufficient for the material to be considered plasma. – DavePhD Feb 26 '14 at 15:22

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I would differ from Xiao because I wouldn't say that a gas and a plasma were the same state of matter, though this is largely terminology.

However this doesn't matter because a flame is not a plasma but a gas phase reaction. So it's just a gas. You mention the Sun, but although the Sun is mostly plasma it isn't a flame in any of the common uses of the word.

Have a look at Confused about fire? for more info.

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John Rennie
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Flames always contain gas, but often include solid particles as well. Solid carbon particles are responsible for the luminous yellow flames of candles and wood fires.

The fraction of the atoms which are ionized (plasma vs gas) is determined by the Saha-Langmuir equation (see J. Appl. Phys. 39, 338 (1968)). There is an equilibrium between ionized and bound states. Give the ionization energy of an element in the flame, temperature, and pressure, the fraction ionized can be determined. At the temperature of common flames, the ionized fraction is low. Alkali metals such as sodium, potassium, etc., which have low ionization energies would have the highest ionized fraction.

Flames can contain molecular radicals such as CH, CC and OH, the emission spectra of which are responsible for the blue color often seen in flames such as hydrocarbon flames.

DavePhD
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Gas and plasma are the same state of matter. So flame = gas = plasma.

Gas and plasma are the same state of matter (meaning belongs to the same phase) since they have the same symmetry. For the same reason, water and vapor are the same state of matter (belongs to the same phase).

Xiao-Gang Wen
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    Can you explain how? – Akshay Nagraj Jan 21 '14 at 10:08
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    gas and plasma are not the same state of matter, see http://en.wikipedia.org/wiki/State_of_matter – gigacyan Jan 21 '14 at 10:20
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    @gigacyan: I think this is a somewhat contentious point. There is not a clear phase transition between a gas and a plasma so it's not obvious they are different states. See http://physics.stackexchange.com/questions/83658/is-there-a-phase-transition-between-a-gas-and-plasma for a discussion of this. If the downvote was yours I think you might have been a bit harsh on Xiao. – John Rennie Jan 21 '14 at 10:37
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    @JohnRennie: one of the downvotes is mine, yes, and I think that it is justified because Xiao simply rejects plasma as the fourth state of matter without any reasoning, so the answer is not really helpful. – gigacyan Jan 21 '14 at 10:43
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    Lots of sources list plasma as the fourth state of matter, after solid, liquid, and gas. (Then there's Boze-Einstein condensate as a 5th state, but that's too off topic for this question). To simply state this isn't so, especially to a 16 year old who has almost certainly seen the 4 states of matter described in his textbooks, is really irresponsible. Give him a chance to learn basic physics before injecting your own view of contentious issues. His books say one thing and you another. How's he supposed to reconcile this at his level? Take it to a different question. – Olin Lathrop Jan 21 '14 at 14:24
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    Here I define states of matter as phases of matter. Symmetry classify states of matter (ie phases of matter). Most High school text books are wrong. It is not my point of view. It is the common sense among physists, if you learn Landau symmetry breaking theory of phases and phase transition. – Xiao-Gang Wen Jan 21 '14 at 14:56
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    In university, when we teach about phases and phase transitions, the first thing we say is that gas and liquid are the same phase. So physics undergraduate all know that saying gas and liquid belong to two different phases is wrong. – Xiao-Gang Wen Jan 21 '14 at 21:06
  • First of all, Science is not a democracy: just because one camp has more people doesn't make that camp right. Second of all, this isn't quite a contentious issue since 1) it is well accepted (well I guess at least in the scientific community and not amongst internet users), 2) it has been tested experimentally, and 3) it is a useful characterization that Landau theory of symmetry breaking gives us a rigorous way of defining (most) phases of matter in terms of broken symmetries. I say most because there exist topological phases beyond Landau theory, but anyway... – nervxxx Jan 23 '14 at 02:45
  • (cont.) most textbooks in the pre-college level aren't too rigorous about making precise statements, they're more concerned with spotting general patterns, and I guess that's the point of those textbooks. I learned in chemistry the octet rule (how atoms with 8 electrons in the outer shell were stable etc.) and various other rules but was utterly dismayed by the tons of exceptions the textbooks always quoted. (Xenon forms compounds etc.) So the bottom line is, one should always be skeptical of anything the textbooks (or anyone) says, and instead one should convince oneself before accepting it – nervxxx Jan 23 '14 at 02:51