Most combustion happens involves the fuels burning in an oxidant. But there seems to be no reason that it cannot happen in the opposite way. Are there any experiments on oxygen burning in hydrogen? Or some oxidant in solid state (like $\ce{KMnO4,KClO3,}$...) burning in a reductive gas?
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3 Answers
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Could you be more clear on what 'burning in' something means? The chemical reactions require both reactants available, so they need to mix - in what sense is Hydrogen mixing and reacting with Oxygen any different that Oxygen mixing and reacting with Hydrogen?
In some sense, we do tend to control these reactions via the fuel, not the oxidant (oxygen free environments are difficult to reproduce on Earth's surface). However there may be some examples of controlling the mixture via restricting the oxidant in a fuel-rich environment... even though I can't even get through the sentence without that sounding wasteful.
Nitrous Oxide
Would you consider the example of Nitrous Oxide injection in an internal combustion engine an example of this? Pre-nitrous, there is compressed atmospheric oxygen and hydrocarbons at a set ratio, and to further increase the burn a nitrous system will inject either NO alone (dry system) or NO and more hydrocarbon fuel (wet system) to add more oxidants that would be available through the 21% Oxygen in the atmosphere.
- The Chemical: https://en.wikipedia.org/wiki/Nitrous_oxide
- Internal Combustion application: https://en.wikipedia.org/wiki/Nitrous
Candles
How about a candle? There's an abundant fuel source (wax), and we frequently control the shape and characteristics of the burn with shaped glass, not to mention put it out via starving it of oxidant.
In either case, if you were to, say take a lump of solid oxygen (nevermind the practical difficulties of dealing with temperatures below 54 Kelvin) and maintained a burn with Hydrogen, what you'd be likely to find would be combustion only happening at the edges, where the oxygen was evaporating and mixing with the reduction agent, similar to lighting a can of gasoline on fire (only the vapors are flammable).
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$\begingroup$ Thanks for reply. For the "burn in" thing. I think that hydrogen comes out from a tube into oxygen or air and have stable flame is a proper scene to characterize the asymmetry in the reaction. So more exactly, if we put a flow of oxygen into hydrogen and ignite it with things like electric discharge, will it have stable flame like the previous case? $\endgroup$– Peter WuCommented Mar 2, 2014 at 6:57
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$\begingroup$ I believe so, yes - however, you will find that getting a room/chamber to be devoid of Oxygen and filled with Hydrogen to be difficult to achieve and maintain (on Earth). $\endgroup$– EhrykCommented Mar 2, 2014 at 16:25
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Are there any experiments on oxygen burning in hydrogen?
(Assuming that burning in "something" describes that "something" is more/at higher concentration than the stuff that is said to burn)
Sure oxygen burns in hydrogen: the upper flammable limit of hydrogen in oxygen is 94 % hydrogen and 6 % oxygen.
Which also tells you one case where such experiments are conducted (measuring flammability for safety sheets).
(For other fuels, the upper flammable limit is much lower, actually fuel concentration < oxygen concentration, so one would rather say the fuel burns in oxygen.)
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You can do a nice experiment burning hydrogen in oxygen, well in air anyway. I have done this many times with a large instant (powdered) coffee tin.
Punch a small hole in the lid and in the base a hole large enough to put in a rubber tube connected to a hydrogen cylinder. Put the tin on a stand with the lid on top, pushed into place to seal the lid but not too securely. Allow the hydrogen into the tin till you judge it has filled it. A couple of minutes.
Light the hydrogen /air mixture at the small hole in the lid.
Turn off the hydrogen supply and wait. Your audience can see the flame burning. When the explosion limit is reached the flame dies and bang; the lid flies off. As it is so light it does no damage.
This illustrates the fact that (a) oxygen/hydrogen mixtures are stable, although the reaction is exothermic the activation barrier is so large that no reaction occurs until some extra energy is supplied (b)That hydrogen burns in air stably at some mixture ratios and (c) that it can explode when the conditions are correct. Its also great fun to do :)
