[tortoise]

hey brothers   :)Help me solve this problem: Why doesn't water burn???

[Mitch]

What would the product be?

H2O + O2 --->   ???

[tortoise]

nothing. but... I think it's not an answer  
I explain that the burn needs oxigen. In the water the a little oxigen (it's only enough for the fish to breath ). So the burn can't tace place in the water. But I don't know whether it's right or wrong  

[Mitch]

That would be the right answer but the wrong reasoning.

[tortoise]

so, please help me  

[jdurg]

For something to 'burn', you need a fuel and an oxidizer.  In most cases, the oxidizer is oxygen but that doesn't always have to be the case.  In explosive compositions, the fuel and oxidizer are either contained in the same compound, or in a mixture of different compounds.  The other requirement for something to burn is that when the fuel and oxidizer combine, they have to form a product, or products, which are more energetically stable than the starting compound(s).  Graphite will burn because CO2 is more energetically stable than Graphite and Oxygen are on their own.  Helium won't burn because any compound it could possibly form would be far less stable than any mixture of Helium and an oxidizer.  Water doesn't 'burn' in the classic sense because water and free oxygen is far more stable than any compound those two could create together.  However, that doesn't mean that water can't burn.

Add some fluorine gas to water and you will see water burn.  This is because the product formed when fluorine and water react is far more energertically stable than pure water and pure fluorine alone.  So in order for things to 'burn', you need three things;

1)  An oxidizer.
2)  A fuel.
3)  Product(s) which is/are more energetically stable than the reactant(s).

[tortoise]

sorry, but i can't understang this sentence (maybe my English is quite bad ): "Graphite will burn because CO2 is more energetically stable than Graphite and Oxygen are on their own"

[jdurg]

That means that the CO2 compound (Carbon dioxide) is more stable than a mixture of Oxygen and Carbon (Graphite) are.

[tortoise]

but in the reaction of water and F2, F2 or water burns?

By the way, please delete the topic "Does water burn?"

[Grumples]

"burning" is a violent reaction between a substance and oxygen (either in elemental form, O2, or taken from some other compound, such as saltpeter, KNO3).  Now, burning is, by definition, a red-ox reaction, and the laws of redox tell us that an atom cannot have an oxidation state that is higher than the number of electrons it can lose to obtain a full octet, or lower than the number of e- it can gain to have a full octet.  Since hydrogen can only gain or lose one electron, its max oxidation state is +1, so in H2O hydrogen can no longer be oxidized.  If you don't know what red-ox is (I didn't learn it in my first year of high school chemistry), then I could explain it in more depth.

Of course, many reactions *look* like a combustion reaction, such as that of flourine gas with, say, iron (or pretty much anything, including water), where the flourine acts just like oxygen would, and it looks as if the iron is burning, but in the technical sense, it isn't really, since no oxygen is involved:

2Fe (III) + 3F2 ----> FeF3 + lots of heat

Also, many reactions (such as iron rusting) would seem to be a combustion reaction; after all, the reaction is the same, whether you are burning iron or just letting it rust. (many people don't realize it, but iron burns very easily: just put a match to some steel wool.  Not very exciting, but the iron's definitely burning).  

Now I could be entirely wrong with my definition of "burn", but the red-ox bit is the reason for water not burning.  

[jdurg]

The re-dox definition is correct.  The definition of 'burning' or 'combustion' doesn't require the presence of oxygen, however.  It only requires the presence of an oxidizer.  (However, in the vast majority of the cases, most 'burning' or 'combustion' takes place with oxygen so people just say that you need oxygen to burn).

In the reaction between F2 and water, water 'burns' because it is what is being oxidized and F2 is what's being reduced.  When something 'burns', it is being oxidized and is the 'fuel'.  The substance being reduced is the 'oxidizer'.  

[tortoise]

Some of my friends suppose that water is the product of combustion (?) so water can't burn !? They say they has never seen any product of combustion which can burn  

[Corvettaholic]

Maybe water can burn. I think I may have posted about this before, but I did a search and couldn't find it. Anyhoo, these people at BlazeLabs said they made COH_h and used that instead of gasoline to power a small electric generator. Will COH_h burn? Its got carbon and hydrogen, and therefore I assume hydrocarbon... but whats the deal with that oxygen in there? If anyone wants the link where I got this from:

http://www.blazelabs.com/n-aquagen.asp

Maybe I posted about this on the HV forums before and forgot to mention it here... I've been very forgetful lately.

[constant thinker]

Corvettaholic,
Ethanol has hydrogen, carbon, and oxygen in it. Throw some vodka on a fire what happens. It burns very fast depending on concentration, but from my expierence very fast. Interesting post made me think Corvettaholic. I'd imagine that your COH_h would burn. It would just requires more oxygen. Ethanol is C₂H₅OH. I'd imagine "burning" it would look something like this:
C₂H₅OH + 6O₂--->2CO₂ + 3H₂O

Correct me if I made a mistake.

[Corvettaholic]

So if it DOES burn, why not make fuel on the fly while driving? The setup they used had a low voltage (50V) high current discharge through water using carbon electrodes. I guess while the water is a plasma the carbon from the electrodes somehow gets fused in with it and you get that new compound. It then bubbles to the surface and you can collect it at a little spout.