What state of matter is fire?

Question

I think it is an energy, but i don't know if I am right.

Answer 1

Hi Crystalfury X.,

No, because energy is not a state of matter, in the sense usually taught in school. (Although they are related by the equation E = mc² , as I'm sure you've heard.)

States of matter include solid, liquid, gas, and plasma. There are a few others, including intermediates (e.g. liquid crystals), some of which exist under very high-tech, extreme conditions (Bose-Einstein condensates, neutron-degenerate matter, and quark-gluon mixes); but for the most part, those first four will answer most states-of-matter questions.

Now, with respect to fire specifically: Flames EMIT energy (light and heat), but you wouldn't say that they ARE energy. Generally fires consist of reacting gas mixtures; they aren't hot enough to be deemed plasma because most of the molecules or fragments are electrically neutral. Exceptions might be electrical-arc containing "fires": a carbon-arc light does burn some carbon, but it's the electrical current that's providing the energy for eventual light emission, and it does get hot enough to have some ionization present. And although wood fires burn a mixture which starts as gas, the yellow color of part of the flame is actually emitted by some ultra-small carbonized solid particles which are formed when the flame reactions strip the hydrogen atoms from the molecules first. Such particles are normally burned up slightly higher up in the flame, unless the supply of air is limited, then you see soot rising from the flame. "Smoke" may be either a slight amount of soot, or rapidly condensing water vapor.

In passing, I should note that most wood- or charcoal-derived flames don't burn completely to CO₂ ; there is usually some CO (carbon monoxide) formed. Kitchen gas stove burners, if they are burning with a double-cone blue flame, are usually harmless in that regard, but don't burn anything else inside an enclosed space, such as your house. CO is rather poisonous, that's why we have working carbon monoxide detectors in our houses!

You might amuse yourself by passing your finger (rapidly!), or a metal spoon, through a candle flame a few times, then smell the resulting sooty layer. It has a characteristic odor of unsaturated-carbonaceous molecules, i.e. those which contain double or triple bonds between the carbon atoms.

If you think a while about why solids and liquids can't burn with a flame, you may realize: they need something that will react with oxygen (usually!), and a source of oxygen. If you have both of these on a molecule in a solid or a liquid, and they decompose, we are likely to characterize the process as an explosion -- the energy release is so concentrated in space that it propagates vigorously through the entire reacting mass, faster than the reaction products can get out of the way. So, in a very short time, all the reaction products are expanding from a very small space, destroying whatever is in their way. And any flash that you see (just before you are blown to bits!) is from the hot reaction products, after the reaction already took place. It would be a stretch to call that a flame, perhaps.

--Cheers, Mr. d.