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If water is heaten up to ridicilously high temperatures, is it possible for the atoms in the molecules to lose their bonds?

And if it is possible, isn't this some kind of chain-reaction?
Like you heat up water --> steam, keep heating it, then wamm you get 1 oxygen and 2 hydrogen atoms, and at that temperature they most likely will self combust creating more heat to make more steam turn into oxygen & hydrogen etc.

Extra question: If you got 1 mole oxygen and 2 mole hydrogen in a container, will it turn into 1 mole water? Or does the pressure matter? Or does the temperature matter?

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3 Answers

up vote 3 down vote accepted

Whenever you have a chemical reaction like $2H_2O \rightleftharpoons 2H_2 + O_2$, it goes both ways. In this reaction, the products on the right have more chemical energy, so going to the right requires energy input, and going to the left releases energy, by the same amount.

Under any conditions, the reaction is running in both directions, but usually at different rates. So in any situation, you will have a predominance of one side over the other. By changing the temperature and/or pressure, you can change the relative reaction rates, but in no case is energy created or destroyed.

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Right, so I understand that having 2 mole hydrogen and 1 mole oxygen in a container won't remain as two seperate gasses for that long. (At room temperature) And as they bond together to water I guess the extra energy that's being released come in the form of heat making the container warmer. –  Harry Svensson Aug 31 '12 at 20:42
@Harry: You have to provide some kind of ignition, but right, it gets a lot warmer :) In fact, that powers rocket engines. –  Mike Dunlavey Sep 1 '12 at 0:56
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Mike's answer is correct that this exchange happens constantly within a system containing water. You are right, however, to suggest that heating water can cause disassociation of water molecules. I am not sure to what temperature you would need to heat steam for this to happen in the absence of other substances, but the explosions at the Fukushima power plant were caused by hydrogen built up from this phenomenon. In that case, the oxygen in the water preferentially bonded with the zinc in the zirconium fuel cladding to form zic oxide; the released hydrogen then collected and, eventually, exploded by recombining with atmospheric oxygen.

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+ Yes. It's important to point out, as you did, that the zirconium stole away the oxygen. –  Mike Dunlavey Aug 30 '12 at 19:39
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If you pour water on a 3000 degree celsius fire it goes boom. Because water dissociates into H2 and O2 before H2 detonates.... That is why firefighters use specially made foams to estinguish these kind of fires.


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Aha, I'd like to know what kind of fires exeed 3000 °C. –  Georg Aug 30 '12 at 21:02
If... this.... fire now exist, doesn't that mean that you could use water as fuel? –  Harry Svensson Aug 31 '12 at 20:45
@Harry: No, because there's no free lunch. The energy you get from the H and O combining was transferred from the hot object into the H and O when the water hit the the object in the first place, thus cooling it off. Think of every problem in terms of energy balance. –  Mike Dunlavey Sep 1 '12 at 1:00
@Georg Dicyanoacetylene + ozone is comfortably above 5000 °C. –  mmc Sep 20 '12 at 17:12
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