The Naked Scientists

The Naked Scientists Forum

Author Topic: Why doesn't water burn?  (Read 24398 times)

Offline tony6789

  • Neilep Level Member
  • ******
  • Posts: 1127
    • View Profile
Re: Why doesn't water burn?
« Reply #25 on: 13/02/2006 14:41:22 »
It will evaporate before it catches flame and coz it's wet

- Big T
 

Offline harryneild

  • Full Member
  • ***
  • Posts: 88
    • View Profile
Re: Why doesn't water burn?
« Reply #26 on: 13/02/2006 17:49:09 »
I think that when two really reactive elements are reacted together there is such a strong bond that it is very hard to break. This is the same for water. Hydrogen and oxygen form strong bonds when reacted and therefore create a rather inert compound because there are few, if any, elements that could displace either the hydrogen or oxygen.
Plumbing tape has Fluorine in it which is amongst the most reactive elements yet the tape is known and used for its ability to not react with water or corrode etc.
 

Offline rosy

  • Neilep Level Member
  • ******
  • Posts: 1018
  • Chemistry
    • View Profile
Re: Why doesn't water burn?
« Reply #27 on: 13/02/2006 17:59:04 »
Running an electric current through water doesn't allow you to burn water... it breaks the water down into hydrogen (H2) and oxygen (O2) which will then recombine (by burning or, if they're mixed initially, explosively) to re-form water.
Water is basically a low energy chemical compound... the electrons are in stable orbitals. You have to put energy in (the electricity) in order to get hydrogen and oxygen, which will then release energy to go back to water.
Hydrogen peroxide (H2O2) can be considered as hydrogen that's been oxidised too far. It wants to oxidise something (take electrons from it) to get down to water.
 

Offline DrDick

  • Sr. Member
  • ****
  • Posts: 162
    • View Profile
Re: Why doesn't water burn?
« Reply #28 on: 31/03/2006 21:01:32 »
Water can burn with the right oxidizer.  Addition of fluorine gas (F2) will cause water to burn, producing OF2 and HF.

The problem (or is it?) is that oxygen is more electronegative (a measure of how much it wants to get and keep electrons) than every other element except fluorine.  Thus, there are only a few compounds out there that can oxidize the oxygen atom in water.

Most people associate burning/oxidation with oxygen.  That is, after all the root of the term "oxidation".  One oxygen atom generally isn't going to oxidize another oxygen atom (although this can happen, resulting in compounds like hydrogen peroxide, where the oxygen is partway between elemental oxygen and normal oxygen found in compounds).

DrDick
 

Offline daveshorts

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 2583
  • Physics, Experiments
    • View Profile
    • http://www.chaosscience.org.uk
Re: Why doesn't water burn?
« Reply #29 on: 31/03/2006 21:57:59 »
Just to jump back a few posts:

Eth Detonation is a bit more complex than that. It is actually where the trigger for each set of molecules to react isn't getting heated up by their neighbours but a supersonic shock wave that is passing through the material. Gunpowder conflagrates - it burns very fast but unless you contain it you don't get a bang, on the other hand TNT if set off with a shockwave (otherwise it jsut burns) will detonate which is a far more violent process.

High explosives detonate, low explosives can just burn very quickly.
 

Offline Hydragurum

  • First timers
  • *
  • Posts: 3
    • View Profile
Re: Why doesn't water burn?
« Reply #30 on: 16/05/2006 05:55:26 »
As an answer to the initial question... if we consider two chemical species, sodium and chlorine for example, both of which have harmful effects, and combine them, there is no reason to suppose that those effects will be more pronounced in the products of the reaction... sodium chloride. Water on the other hand is a molecular species. There is no real correlation between the nature of the reactions of a reaction with the products. However, when something burns in oxygen, it is essentially a combustion reaction. That is... water and carbon dioxide (or carbon monoxide depending on the availibility of oxygen) are the products. So in other words, you can't necessarily predict the nature of some products by simply comparing the nature of the reactants. I mean... who knows what kind of chemical properties... say... ytterbium dichromate has? No one does until they carry out an actual reaction and perform measurements. I hope that helped.

Gideon Dunkley 111
 

Offline Hydragurum

  • First timers
  • *
  • Posts: 3
    • View Profile
Re: Why doesn't water burn?
« Reply #31 on: 16/05/2006 06:01:49 »
Sorry for the double post...

quote:
Originally posted by harryneild

I think that when two really reactive elements are reacted together there is such a strong bond that it is very hard to break. This is the same for water. Hydrogen and oxygen form strong bonds when reacted and therefore create a rather inert compound because there are few, if any, elements that could displace either the hydrogen or oxygen.
Plumbing tape has Fluorine in it which is amongst the most reactive elements yet the tape is known and used for its ability to not react with water or corrode etc.



That is essentially correct. Since the bond with hydrogen and oxygen is a polar covalent bond and the molecule overall as a whole is polar, the overall amount of energy required to break the intramolecular covalent bonds is substantial. Nevertheless, there are compounds that will react with water to displace it... such as the alkali metals. Water can also be either reduced or oxidized in a galvanic cell to give oxygen gas and hydrogen ions. On the other hand, if water is reduced, you get hydrogen gas and hydroxide ions. Good observation Harry.

Gideon Dunkley 111
 

Offline dynamix

  • First timers
  • *
  • Posts: 3
    • View Profile
Re: Why doesn't water burn?
« Reply #32 on: 30/05/2006 04:12:35 »
Here's an interesting little "burning water" link...

A guy in New Zealand is claiming to have invented a process that can be applied to water, which gives it the burning properties of a hydrocarbon, so it can be used to power motor vehicles. This video shows him using it to power his own motorcycle. Thing is, he then goes on to show an experiment where he puts a little water into a balloon, inflates it, and then uses a flame to burst the ballon and ignite the water!

newbielink:http://waterpoweredcar.com/BNE_cosmicwatercell_hq.wmv [nonactive]

Now, anyone can try this experiment at home, and I'm told it does work. I am convinced, however, that there is some faulty science at work here. See if you agree with me...

Clue #1: The balloon is inflated by mouth, hence providing a CO2 rich medium for the water.

Clue #2: Popping an inflated balloon with a flame simultaneously supplies the "reactants" with heat, explosive decompression and a large surface area.

Clue #3: The guy's motorcycle is still producing CO & other pollutants which you would expect to see from burning hydrocarbons.

This is what I think is happening. See if any of you agree. (If you don't, I would be interested to hear your take on it.)

Theory: H2O is placed in an environment which is then pressurised with a CO2-rich gas. The combination, then, of explosive decompression and heat from the flame (possibly catalysed by the large surface area of the balloon itself) reacts some of the H2O with the some of the CO2 to produce a trace amount of Ethanol, which then burns.

Am I right? Am I close? I'd love to hear your views.

Thanks

"What's a unified theory, daddy?"...
"Ask your mother!"
 

Offline rosy

  • Neilep Level Member
  • ******
  • Posts: 1018
  • Chemistry
    • View Profile
Re: Why doesn't water burn?
« Reply #33 on: 30/05/2006 14:32:15 »
Mmm. Having had a look at the website, it seems to be a perpetual motion machine. So I'm inclined not to believe in it. On the other hand, the guy talking on the video seems to think it runs on God-power so maybe it's just a miracle.
My first hypothesis about what's going on with the car in the video is that the car's battery's hydrolysing water and the power's coming from the hydrogen that creates.. so the engine's just running on the battery.
I can't find/don't have time to look for instructions for repeating the water/balloon thing. It looks awfully like some kind of alcohol when it's burning, but maybe that's just me..
 

The Naked Scientists Forum

Re: Why doesn't water burn?
« Reply #33 on: 30/05/2006 14:32:15 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums