You can't burn water, because it's already burnt

arcrust@lemmy.ml to Showerthoughts@lemmy.world – 373 points –

Fire is the rapid oxidation of a material. Water is 2 hydrogen and 1 oxygen. Every molecule is fully oxidized. It's also a common byproduct of fire. Therefore, you can't burn it, because it's already burnt

50

You are viewing a single comment
View all comments

Oh man... Wait until you hear about fires hot enough that if you put water on then, it breaks the water molecule and the hydrogen molecules cause an explosion.

Look up class D fires.

Furthermore, you can burn water with a strong enough oxidizer. Oxygen, despite lending its name to the word "oxidize", is not the best oxidizer out there. That belongs to things with fluorine in it. You can burn water with pure fluorine gas to produce hydrogen fluoride and oxygen.

Don't try this at home. Both fluorine and the resulting HF is deadky.

HF is itself a super nasty piece of work -- a deadly acid that seeps through your skin and kills you from the inside.

The fun part about that: you can burn hydrogen with fluorine because fluorine is the best oxidizer; it's then deadly (and caustic) because hydrogen is not the best reducer - it's both an oxidizer and a reducer and, as a result, it's basically middle-of-the-road for both properties. Specifically, most metals are better. So the HF will happily drop its hydrogen for many metals to oxidize (fluoridate) them instead. Lead, iron, zinc, aluminum, magnesium, and lithium will each make a way more stable fluoride than does hydrogen.

In solution (say, if you inhale HF, it'll dissolve into the moisture in your lungs), it breaks apart into H⁺ and F⁻ ions - both of which are just straight-up electrochemically promiscuous. The pair'll run through your lungs breaking up organic bonds like couples at an orgy.

Even so, HF doesn't hold a candle in terms of danger (and oxidation potential) compared to fluorine peroxide / dioxygen difluoride / FOOF.

That looks like even more fun than chlorine trifluoride

There's always a lower energy state

Flourine by itself is nothing compared to chlorine triflouride (CTF) though.

There were some ideas to use it in rockets, but, as John D. Clark put it:

It is, of course, extremely toxic, but that's the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water—with which it reacts explosively. It can be kept in some of the ordinary structural metals—steel, copper, aluminum, etc.—because of the formation of a thin film of insoluble metal fluoride that protects the bulk of the metal, just as the invisible coat of oxide on aluminum keeps it from burning up in the atmosphere. If, however, this coat is melted or scrubbed off, and has no chance to reform, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes.

There were a few successful test fires with a CTF rocket on the ground, but to avoid explosions they had go through an elaborate multiple hour long cleaning procedure, and it ended up being too expensive and dangerous.

Ah so it's hot enough to electrolyze water and then when the hydrogen and oxygen gas move out of that heat zone, they're still in a hot enough area to re-oxidize into water, burning the hydrogen. Neat.

Nothing about this makes sense. Is it reoxidizing or burning?

Yes.

Not only will metal fires break apart the water into oxygen and hydrogen, but they will consume the oxygen, as the metal oxide is a more stable energy state than is water. So you end up with a billow of hydrogen coming off the fire that mixes with the oxygen just above (because lighter gases rise) the oxygen-depleted zone of the fire, and it combusts there.

There was some other thread talking about invisible fire produced by burning a particular gas... imagine getting burned and not being able to identify the source

You’re probably referring to methanol fires! Commonly used as a fuel for things like F1 cars, iirc.

Hydrogen fires have the same characteristic as i understand it