Light/Heat "Fire" without oxidization?

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webgiant
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Light/Heat "Fire" without oxidization?

Postby webgiant » Fri Nov 05, 2010 4:24 am UTC

I was just discussing fire and combustion chemistry with a few friends, and the concept of non-oxidization "fire" came up. That is, while a fire producing heat and light requires fuel, oxygen, and ignition, is it possible to create a reaction which uses fuel and ignition, but no oxygen, to produce heat and light?

None of us could come up with such a reaction, but I thought I'd ask here and see if any chemists here knew of such a reaction.

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Re: Light/Heat "Fire" without oxidization?

Postby jmorgan3 » Fri Nov 05, 2010 4:27 am UTC

Just about any explosive.
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Re: Light/Heat "Fire" without oxidization?

Postby ajd007 » Fri Nov 05, 2010 5:21 am UTC

Thermite is self-oxidizing:

Fe2O3 + 2Al → 2Fe + Al2O3 + heat

http://en.wikipedia.org/wiki/Thermite

This also makes it pretty much impossible to put out once it starts burning

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Re: Light/Heat "Fire" without oxidization?

Postby 2.71828183 » Fri Nov 05, 2010 5:29 am UTC

If by oxygen you mean gaseous oxygen, thermite comes to mind as a good example, particularly because it reacts slowly enough that you can see it, rather than just being there one second and gone the next. The solid iron oxide and aluminum mixture can burn without any gaseous oxygen because the oxidizer is already there, bound up with the iron.

If you don't want oxygen to be involved at all, you could (hypothetically) burn sodium metal in chlorine gas to make sodium chloride salt, or burn a variety of things in fluorine gas, etc. There are plenty of reactions that don't require oxygen and are exothermic enough to produce heat and light; oxygen is just a common oxidizer because a good portion of our atmosphere happens to be made of it (and, relatedly, that we run on it, so it's not toxic for us to handle).

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Re: Light/Heat "Fire" without oxidization?

Postby Minerva » Fri Nov 05, 2010 8:00 am UTC

webgiant wrote:I was just discussing fire and combustion chemistry with a few friends, and the concept of non-oxidization "fire" came up. That is, while a fire producing heat and light requires fuel, oxygen, and ignition, is it possible to create a reaction which uses fuel and ignition, but no oxygen, to produce heat and light?


There are lots of other fuel + oxidiser systems of chemicals that will burn, where the oxidiser is not necessarily oxygen.

The violent reaction of hydrogen gas and chlorine gas, triggered by UV light, for example. Or, the hypergolic ignition of acetylene in a chlorine atmosphere.

Sodium violently burning when introduced into a chlorine atmosphere. Aluminium violently "burning" when introduced into bromine.

Or iron burning when heated and put into an atmosphere of fluorine or chlorine.

Also, look at hypergolic rocket propellants, for example hydrazine and nitrogen tetroxide, or furfural alcohol and nitric acid.
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Re: Light/Heat "Fire" without oxidization?

Postby Mr_Rose » Fri Nov 05, 2010 10:29 am UTC

You might also want to look at the "interesting chemicals" thread; there are lots of crazy-powerful oxygen-free oxidisers out there. Particularly Chlorine Trifluoride.
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Re: Light/Heat "Fire" without oxidization?

Postby Tass » Fri Nov 05, 2010 11:12 am UTC

Or FOOF

Edit: Do'h obviously not oxygen free, but powerful.

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Re: Light/Heat "Fire" without oxidization?

Postby webgiant » Fri Nov 05, 2010 2:12 pm UTC

Y'all are coming up with a lot of fun little reactions, but remember that the instant your "recipe" uses the term "oxidization", oxygen is involved. Oxidize does mean, in very basic terms, "combine oxygen with it".

The idea was a combustion-type reaction, but as combustion, fire, flame, etc. on Earth have become synonymous with "oxygen catalyzed reactions" or oxidization, the idea was a light/heat reaction that did not involve oxygen in any way: a "fire" with fuel and ignition but no oxygen.

My original non-board discussion dealt with exoplanets which might have life on them not based on carbon, and thus possibly not including oxygen in their chemical reactions. So we were wondering what the chlorine or silicon-based life forms would be sitting around, roasting stuff on and singing "campfire" songs around, during the first few thousand years of their sentient existence.

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Re: Light/Heat "Fire" without oxidization?

Postby Velifer » Fri Nov 05, 2010 2:18 pm UTC

Tass wrote:Or FOOF

Hydrogen sulfide, for example, reacts with four molecules of FOOF to give sulfur hexafluoride, 2 molecules of HF and four oxygens. . .and 433 kcal

Please tell me that's per mole, 'cause otherwise...

433Kcal * 6.02·1024 / 70g·mol-1 = 2.6x1027 Kcal/g

This is pretty basic conversion factor stuff, so either my brain is broken doing the conversions, or my brain just broke looking at the answer. Whipping kilocalories into TNT equivalents: 2,601,739,972,000,000,000 kilotons of TNT from one gram?

Where's my error, cause that's too bizarre to be believed.
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Re: Light/Heat "Fire" without oxidization?

Postby gmalivuk » Fri Nov 05, 2010 2:41 pm UTC

webgiant wrote:Y'all are coming up with a lot of fun little reactions, but remember that the instant your "recipe" uses the term "oxidization", oxygen is involved. Oxidize does mean, in very basic terms, "combine oxygen with it".
No, it doesn't. Rather, it means the loss of electrons or increase in oxidation state. The name is just the result of oxygen being the most common element that shows up in oxidizers. The halogens tend to be good oxidizers as well, for example.
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Re: Light/Heat "Fire" without oxidization?

Postby frezik » Fri Nov 05, 2010 4:00 pm UTC

webgiant wrote:My original non-board discussion dealt with exoplanets which might have life on them not based on carbon, and thus possibly not including oxygen in their chemical reactions. So we were wondering what the chlorine or silicon-based life forms would be sitting around, roasting stuff on and singing "campfire" songs around, during the first few thousand years of their sentient existence.


The problem I see here is that oxygen is both incredibly reactive and relatively abundant. There would almost certainly be oxygen somewhere on their world, and that oxygen would easily take the place of something else in their chemistry.

In a hypothetical world where the oxygen has somehow disappeared or been sequestered, introducing even small amounts of oxygen (like from an asteroid impact) would be extremely toxic.

Everything above applies to carbon, too. It's reactivity and abundance are major reasons why we tend to assume any life will be based on carbon, oxygen, and water.

For a fun/dangerous use of nitrate fertilizer to provide oxygen without relying on atmospheric gases, see:

http://www.nsa.gov/public_info/_files/tech_journals/emergency_destruction.pdf
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Re: Light/Heat "Fire" without oxidization?

Postby cjameshuff » Fri Nov 05, 2010 9:49 pm UTC

frezik wrote:The problem I see here is that oxygen is both incredibly reactive and relatively abundant. There would almost certainly be oxygen somewhere on their world, and that oxygen would easily take the place of something else in their chemistry.


Indeed, roughly a third of Earth's mass is actually oxygen, and it's likely that figure's below average for Earth-sized bodies due to the event that formed the moon. That sandy beach? About two out of every three atoms is oxygen, a bit over half the sand's composition by mass. Any terrestrial planet or inhabited moon is practically guaranteed to be covered with materials that are mostly made of oxygen. And unlikely to be so depleted in carbon that life on the surface wouldn't quickly make use of it...though something that doesn't use carbon might be more likely than something that doesn't use oxygen. Chlorine, in contrast, is rather rare...concentrated over time to about 1.9% by mass in Earth's oceans.

Perhaps sulfur. It's not as common as oxygen, but fairly common (few percent of the Earth) and can be concentrated at a planetary surface by natural processes (look at Io), and it's a decent oxidizer (look at zinc-sulfur rocket fuel for an example of stuff burning with it). Maybe some kind of high temperature life could use it...

edit: my source for the elemental abundances of Earth is http://www.ncbi.nlm.nih.gov/pmc/articles/PMC350422/
Table on the third page. Iron is 32.07%, oxygen is 30.12%, silicon 15.12%, magnesium 13.9%...that's 90-some percent of the planet right there. And carbon's about 22 times as abundant as chlorine...and I would suspect the difference is much bigger at the surface, a lot of carbon being released as CO2 in volcanism, while chlorine is relatively happy sticking around in minerals underground.

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Re: Light/Heat "Fire" without oxidization?

Postby Soralin » Sat Nov 06, 2010 12:09 am UTC

cjameshuff wrote:
frezik wrote:The problem I see here is that oxygen is both incredibly reactive and relatively abundant. There would almost certainly be oxygen somewhere on their world, and that oxygen would easily take the place of something else in their chemistry.


Indeed, roughly a third of Earth's mass is actually oxygen, and it's likely that figure's below average for Earth-sized bodies due to the event that formed the moon. That sandy beach? About two out of every three atoms is oxygen, a bit over half the sand's composition by mass. Any terrestrial planet or inhabited moon is practically guaranteed to be covered with materials that are mostly made of oxygen. And unlikely to be so depleted in carbon that life on the surface wouldn't quickly make use of it...though something that doesn't use carbon might be more likely than something that doesn't use oxygen. Chlorine, in contrast, is rather rare...concentrated over time to about 1.9% by mass in Earth's oceans.

Perhaps sulfur. It's not as common as oxygen, but fairly common (few percent of the Earth) and can be concentrated at a planetary surface by natural processes (look at Io), and it's a decent oxidizer (look at zinc-sulfur rocket fuel for an example of stuff burning with it). Maybe some kind of high temperature life could use it...

edit: my source for the elemental abundances of Earth is http://www.ncbi.nlm.nih.gov/pmc/articles/PMC350422/
Table on the third page. Iron is 32.07%, oxygen is 30.12%, silicon 15.12%, magnesium 13.9%...that's 90-some percent of the planet right there. And carbon's about 22 times as abundant as chlorine...and I would suspect the difference is much bigger at the surface, a lot of carbon being released as CO2 in volcanism, while chlorine is relatively happy sticking around in minerals underground.

A bit of a nitpick: Looking at the chart, the rest of the atoms are in parts per million, or billion, so that's probably that 30% of Earth's atoms are oxygen, not necessarily 30% of it's mass, but the number of atoms of it is probably the more important number here. (also, just looking at wikipedia, if you look at just the Earth's crust, that number goes up to over 46% of the atoms in it being oxygen)

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Re: Light/Heat "Fire" without oxidization?

Postby cjameshuff » Sat Nov 06, 2010 1:33 am UTC

Soralin wrote:A bit of a nitpick: Looking at the chart, the rest of the atoms are in parts per million, or billion, so that's probably that 30% of Earth's atoms are oxygen, not necessarily 30% of it's mass, but the number of atoms of it is probably the more important number here.


That doesn't follow. Parts per million/billion aren't any more specific to molar measurements than parts per hundred (percent) are, and when molar ratios are used, it's usually mentioned (unless it's obvious what's meant from context).

Soralin wrote:(also, just looking at wikipedia, if you look at just the Earth's crust, that number goes up to over 46% of the atoms in it being oxygen)


Oxygen is 53% of the mass of silica, 40% of the mass of MgO, and 47% of the mass of alumina. Considering how much of the iron ended up in the core, the crust being 46% oxygen by mass does not seem like much of a stretch.

http://en.wikipedia.org/wiki/Abundances ... (data_page)
CRC Handbook: 46.1%...likely the origin of your figure. Table's labeled as mass fraction.

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Re: Light/Heat "Fire" without oxidization?

Postby Coffee » Sat Nov 06, 2010 2:37 am UTC

Would the fusion of hydrogen into helium count? It doesn't require the presence of atmospheric oxygen.
*edit* nevermind. Doesn't meet the criteria of fuel and ignition.
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Re: Light/Heat "Fire" without oxidization?

Postby dainbramage » Sat Nov 06, 2010 3:18 am UTC

I think a good example would be the burning of a typical double-base rocket fuel. Essentially a bunch of nitrocellulose dissolved into nitroglycerin, but it burns much more slowly than either of the individual components. It's just a decomposition reaction, but produces what very much appears a flame. In an atmosphere, CO produced will further combust, but it works in a vacuum, and certainly looks like a typical 'flame'.

Of course, most modern high explosives are simply decomposition reactions, which produce heat and light (as well as a large volume of gas in what was previously a small volume of solid).

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Re: Light/Heat "Fire" without oxidization?

Postby Tass » Sat Nov 06, 2010 8:54 am UTC

webgiant wrote:The idea was a combustion-type reaction, but as combustion, fire, flame, etc. on Earth have become synonymous with "oxygen catalyzed reactions" or oxidization, the idea was a light/heat reaction that did not involve oxygen in any way: a "fire" with fuel and ignition but no oxygen.


Well as gmalivuk pointed out you use the terms wrong. But what you ask for here is definitely possible. A regular candle will burn just fine in a chlorine atmosphere. It is still an "oxidation" by the common definition, but there is no oxygen present.

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Re: Light/Heat "Fire" without oxidization?

Postby arbitrary value » Sat Nov 06, 2010 9:27 am UTC

One interesting reaction to consider is the decomposition of hydrazine (N2H4) into nitrogen gas (N2) and hydrogen gas (H2). It's quite exothermic and "fiery" but is not your everyday fuel+oxidizer reaction. It is still technically a redox reaction (most things are).

The problem I see here is that oxygen is both incredibly reactive and relatively abundant.


This is somewhat deceptive. Oxygen is indeed both reactive and abundant, but because it is so reactive, it is usually locked away in very stable chemical bonds, such as those to silicon in sand. If you were traveling to another planet, you would be very unlikely to find oxygen gas in its atmosphere because that oxygen would have all reacted with some other chemical long ago.

Earth does have an oxygen-rich atmosphere, but this is almost entirely due to living things carrying out photosynthesis. Before the evolution of photosynthesis, all that free oxygen in the atmosphere was in carbon dioxide molecules instead.

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Re: Light/Heat "Fire" without oxidization?

Postby cjameshuff » Sat Nov 06, 2010 4:20 pm UTC

arbitrary value wrote:This is somewhat deceptive. Oxygen is indeed both reactive and abundant, but because it is so reactive, it is usually locked away in very stable chemical bonds, such as those to silicon in sand. If you were traveling to another planet, you would be very unlikely to find oxygen gas in its atmosphere because that oxygen would have all reacted with some other chemical long ago.


The same goes for other oxidizers, though. If an atmosphere is reactive enough to sustain fire with fuels common on the surface, both need something to constantly recycle them. The same goes for strong solid or liquid oxidizers in a reducing atmosphere...

The subject appears to be about life bearing worlds, with atmospheres likely modified by native life. If you sequestered all oxygen on Earth as solid and liquid compounds and liberated all the chlorine in the oceans and surface portions of the crust as gas, I doubt you'd get an atmosphere that could sustain fire. The abundance of oxygen compounds (particularly water and carbon oxides) makes it likely that life-generated oxidizing atmospheres will contain oxygen.

An aside, the other two terrestrial worlds in our solar system that have atmospheres have ones of largely CO2. Few things will burn in CO2, but it is still an oxidizer. Magnesium metal is one...I don't know of any more biologically accessible reducing agents that would be strong enough.

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Re: Light/Heat "Fire" without oxidization?

Postby Soralin » Sat Nov 06, 2010 4:34 pm UTC

cjameshuff wrote:
Soralin wrote:A bit of a nitpick: Looking at the chart, the rest of the atoms are in parts per million, or billion, so that's probably that 30% of Earth's atoms are oxygen, not necessarily 30% of it's mass, but the number of atoms of it is probably the more important number here.


That doesn't follow. Parts per million/billion aren't any more specific to molar measurements than parts per hundred (percent) are, and when molar ratios are used, it's usually mentioned (unless it's obvious what's meant from context).

Ah yeah, I made that connection, but only in one direction, converting from % -> ppm, rather than the other way around. It just seemed a bit unusual to have ppm refer to mass, rather than quantity.

That would mean there's quite a bit more oxygen atoms than that, as a percentage of atoms, given how light oxygen is, as an atom, compared to the others that make up a significant fraction of the Earth's mass.

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Re: Light/Heat "Fire" without oxidization?

Postby cjameshuff » Sun Nov 07, 2010 1:20 am UTC

Soralin wrote:That would mean there's quite a bit more oxygen atoms than that, as a percentage of atoms, given how light oxygen is, as an atom, compared to the others that make up a significant fraction of the Earth's mass.


Well, look at http://en.wikipedia.org/wiki/Silicate_m ... ilicates...
Silica is SiO2, alumina is Al2O3, silicates add one or two oxygens per silicon atom and often have a big mess of silicate anions per cation...take the feldspars, generally things like: KAlSi3O8. Limestone, marble, chalk? CaCO3. Rock is pretty much oxygen being held together by various other things.

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Re: Light/Heat "Fire" without oxidization?

Postby webgiant » Sun Nov 07, 2010 2:21 pm UTC

gmalivuk wrote:
webgiant wrote:Y'all are coming up with a lot of fun little reactions, but remember that the instant your "recipe" uses the term "oxidization", oxygen is involved. Oxidize does mean, in very basic terms, "combine oxygen with it".
No, it doesn't. Rather, it means the loss of electrons or increase in oxidation state. The name is just the result of oxygen being the most common element that shows up in oxidizers. The halogens tend to be good oxidizers as well, for example.


I did say in very basic terms, meaning that without a qualifier (a non-basic term) on Earth oxidizing is going to be a reaction involving oxygen. The roots of oxidize are in the word "oxygen".

If you're going to get complicated then we're no longer talking in very basic terms, are we. :P :wink:

Tass wrote:
webgiant wrote:The idea was a combustion-type reaction, but as combustion, fire, flame, etc. on Earth have become synonymous with "oxygen catalyzed reactions" or oxidization, the idea was a light/heat reaction that did not involve oxygen in any way: a "fire" with fuel and ignition but no oxygen.


Well as gmalivuk pointed out you use the terms wrong. But what you ask for here is definitely possible. A regular candle will burn just fine in a chlorine atmosphere. It is still an "oxidation" by the common definition, but there is no oxygen present.

Okay so using the more complicated definition of oxidize as "reactions not involving oxygen, the word from which we derive 'oxidize'", what sort of fuel might develop in a chlorine atmosphere without any oxygen not freely available in the atmosphere? Saying a candle burns fine in a chlorine atmosphere is all fine and good, but the candle is the result of an ecology involving oxygen.

Just trying to flesh out our chlorine creatures' campfire scenario.

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Re: Light/Heat "Fire" without oxidization?

Postby arbitrary value » Sun Nov 07, 2010 2:58 pm UTC

I think a chemist would not assume by default that oxidation referred to a reaction with oxygen.

I'm not personally familiar with this specific sort of chemistry, but I see no reason why the same sort of hydrocarbons that we burn in oxygen on Earth wouldn't burn in chlorine. Consider, for example, propane:

C3H8 + 10 Cl2 -> 3 CCl4 + 8 HCl

The heats of formation (kJ/mol) are as follows:
CCl4 -139.5
HCl -92.30
C3H8 -104.7
(Cl2 is of course zero)

Thus, burning a mole of propane in chlorine gas would release 1052.2 kJ of energy.

Compare this to burning in oxygen:

C3H8 + 5 O2 -> 3 CO2 + 4 H2O

CO2 -393.509
H20 -285.83

This releases 2219.147 kJ of energy per mole of propane; about twice as much as burning in chlorine did.

On the other hand, burning in fluorine releases more energy than burning in oxygen.

C3H8 + 10 F2 -> 3 CF4 + 8 HF

CF4 -925
HF -269

This releases 4927 kJ of energy per mole of propane; my naive guess is that this is because in terms of electronegativity, Cl < O < F. Fluorine is nasty stuff... Wikipedia puts it nicely: "For example, it will readily "burn" hydrocarbons at room temperature, in contrast to the combustion of hydrocarbons by oxygen, which requires an input of energy with a spark." In fact, fluorine can oxidize chlorine to release energy.

(I got the enthalpies of formation off of the internet; if you wanted a scientifically valid calculation, you'd have to look them up in a real table. I also apologize for any arithmetic errors I may have made.)

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Re: Light/Heat "Fire" without oxidization?

Postby cjameshuff » Sun Nov 07, 2010 5:47 pm UTC

webgiant wrote:
gmalivuk wrote:
webgiant wrote:Y'all are coming up with a lot of fun little reactions, but remember that the instant your "recipe" uses the term "oxidization", oxygen is involved. Oxidize does mean, in very basic terms, "combine oxygen with it".
No, it doesn't. Rather, it means the loss of electrons or increase in oxidation state. The name is just the result of oxygen being the most common element that shows up in oxidizers. The halogens tend to be good oxidizers as well, for example.


I did say in very basic terms, meaning that without a qualifier (a non-basic term) on Earth oxidizing is going to be a reaction involving oxygen. The roots of oxidize are in the word "oxygen".


The root of the word is a historical quirk. Oxidation does not require oxygen. This isn't a subtle detail of the terminology. Plus, we are specifically discussing planets other than Earth, with combustion reactions that do not involve elemental oxygen. Objecting that we are involving oxygen the moment we use the term oxidation is simply incorrect.


webgiant wrote:Okay so using the more complicated definition of oxidize as "reactions not involving oxygen, the word from which we derive 'oxidize'", what sort of fuel might develop in a chlorine atmosphere without any oxygen not freely available in the atmosphere? Saying a candle burns fine in a chlorine atmosphere is all fine and good, but the candle is the result of an ecology involving oxygen.


Well, that ecology is freakishly improbable, due both to the scarcity of chlorine in the universe and to its tendency to form stable solid compounds and highly reactive gases (an equivalent to the carbon cycle seems unlikely), but it seems likely it'd be based on organic chemistry in water and produce hydrocarbon and carbohydrate fuels.

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Re: Light/Heat "Fire" without oxidization?

Postby gmalivuk » Mon Nov 08, 2010 4:58 pm UTC

Yeah, the historical origin is irrelevant. "Oxidization" no more necessarily requires oxygen than "hydrogen" necessarily has anything to do with water.

(I mean, hell, "oxygen" itself means creating acid. So much for words that originated before we knew much about their referents...)
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