Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: DoctorBeaver on 03/12/2005 02:02:26
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Both oxygen & hydrogen are highly flammable, so why isn't water? What is the actual process that stops it burning?
(I dare anyone to say "coz it's wet"!)
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Put a piece of sodium in contact with water and it fizzes like mad. Stand in a room full of chlorine gas and your face burns off. But table salt isn't dangerous.
(Oh, sorry, it is, so my arteries have just told me.[:D])
Anyway, in what way is oxygen "flammable"?
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Anyway, in what way is oxygen "flammable"?
OK, correction - it aids combustion
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well, water is already burned :)
It`s derived by burning hidrogen :)
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It`s derived by burning hidrogen :)
Is it?
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From the doc. Why doesn't water burn?
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Doc. I maybe stating the obvious here,but it does if its hot.
Are you a believer in Empirical studies.
Just a tip though if you are, if your left handed then use your right hand.
And please be careful, you don't want to ruin your watch now do you[:D][:D][:)]
Michael (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Frofl.gif&hash=481319b762ee9d57cda15e90d2e83ee6)
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Just a pedantic point - water doesn't burn, it scalds[:o)]
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Originally posted by DoctorBeaver
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It`s derived by burning hidrogen :)
Is it?
Yes. Yes it is .
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I never knew that. Thank you
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But if burning hydrogen produces water, why didn't the Hindenberg put itself out?
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ok lets forget the insanity of this seconary question the bond is too strong for the hydrogen to comust or so im told after my friend caught me with a blowtorch attacking a shot glass of water, well ok thats anicdotal evidance but the real question was why cant we simply make the sea burn? without the help of a Shell oil spillage?
Is that the mouthwash in your eyes?
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I don`t understand what did you want to say with Hindenberg ?
2H2 + O2 = 2H2O
If we define combustion as oxidation, than if we would like to inflame water :
2H2O + 02 = 4HO in whitch hidrogen is +2, but this is very unstable, and doesn`t exist.
C + O2 = CO2 and we can`t inflame CO2 either. However, like water, it is great extinguisher.
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Ok, I remembered something meanwhile ...
It`s caled Hydrogen peroxide H2O2, so I guess it can burn. :)
Even so, Hydrogen is here +1 and Oxigen -1.
I`m not sure anymore ... :(
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Darko - take a deep breath! [:D]
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Why didn't the Hindeberg put itself out? I'm just guessing, but maybe it's because it didn't produce a dense enough concentration of water when the H and O reacted? (You can still light a fire in a moist atmosphere. But not underwater. I think.)
And when H reacts with O, doesn't it just "pop" rather than burn with a flame? So the burning of the Hindenberg was the burning of the materials making up the airship, ignited by the "pop".
And as for why doesn't water burn, isn't it to do with the enthalpy of reaction or something like that. (Forgive me, I've forgotten all my Chemistry - I'm going back 20 years now. This is hurting my brain. I'm out of my depth here. I think I'll go back to the non-chemistry forums now.)
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I'm out of my depth here. I think I'll go back to the non-chemistry forums now.)
I think I'd best go back to Tellytubbyland [V]
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Originally posted by Solvay_1927
And when H reacts with O, doesn't it just "pop" rather than burn with a flame? So the burning of the Hindenberg was the burning of the materials making up the airship, ignited by the "pop".
You'd better tell the people who design the rocket engines for the space shuttle about this then – they believe their engines burn hydrogen and oxygen.
The difference between burning or going 'pop' (or even going 'bang') depends upon whether the fuel (hydrogen) and the oxidiser (oxygen) is premixed, or whether it mixes as it burns, and so maintains a constant flame as the mixture progresses.
I have heard various points about the Hindenburg. One thing that I have heard (although I would not claim to be authoritative on the subject) is that because hydrogen is lighter than air, there would have been very little flame beneath the hydrogen tanks, all of it being directed upwards. That would not have prevented blast from being blown downwards, but the only flame beneath would then have been that produced by fuel for the engines, and other flammables beneath the buoyancy tanks. The other thing the passengers would have had to contend with is simply the fall to the ground.
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The Hidenberg tragedy occured because of a simple electric discharge.
But the temperature of an electric charge is so high that even a gas as inert as nitrogen reacts at that temperature.Water can also be prepared with an electric discharge so can it be made to break up.
Electrolysis.....that is the burning of water technically..
lobo
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A couple of minor clarifications supplied to me by a neighbour who was a fireman.
Water or CO2 do not put out fires directly. Principally water is dispensed to remove the heat from a fire by vaporization, and CO2 deprives the fire of oxygen by displacement.
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water didnt put out the airship because it was most likely created in the form of a gas (water vapour) because of the heat created by the explosion. Even if it was formed in the liquid state it would not be able to stop the explosion as it happened too fast (and too little was formed anyway). The reason that water doesnt burn is because as mentioned before it has a lot less energy than hydrogen and oxygen seperatley (its the product of an exothermic reaction so it must have less energy than the reactants) this means its less reactive and stable enough to prevent it from combustion.
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The original question betrays a fundamental lack of understanding of the physical difference between compounds, and mixtures of the components that form compounds.
When various materials react to form compounds, there is an energetic change as chemical bonds are formed between the materials that form the compound In the case of hydrogen and oxygen forming water this is called Exothermic because it releases a lot of energy which you experience as the heat of a flame as a jet of hydrogen gas burns in an atmosphere of oxygen (or air)to form water. The falme burns quietly because the mixing of the hydrogen and oxygen is controlled
If you mix hydrogen (or light hydrocarbons) and oxygen (or air which has a fair bit of oxygen in it) and then set light to it with a spark you get a big explosion brcasue the burning is fast and uncontrolled.
Note it is not essential for energy to be released as compounds are formed. The process of combining hydrogen with nitrogen to make ammonia needs the input of a lot of energy so inorder to form that you need a lot of heat and pressure to make it. When the ammonia is formed however it is still a reasonably stable although chemically active compound. such reactions are called endotherrmic because they absorb energy when they take place.
Just one final comment. As these pages seem to be a bit obsessed with explosives. If you want to make an explosive you mix together solids that have exothermic reactions with other solids to produce gasses. Detonation is just the process that you use to start the reaction which will then sustain itself. this can happen with anything from the slightest touch or disturbance to an extemely violent shock wave. The best explosives are those that explode in predictable and controllable ways when dujected to quite a violent shock as a detonator.
Learn, create, test and tell
evolution rules in all things
God says so!
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The original question betrays a fundamental lack of understanding ...
Well that's you told, Eth! Posting a question that you don't already know the answer to! Honestly! Go to the back of the class! [;)]
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Reading my last reply now that I'm sober ([:I]), I realise it might sound like I was having a go at Ian. Apologies to Ian if it came across the wrong way.
(Ian's answer above is very clear and useful. Although, I suppose the opening is rather blunt...)
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Well that's you told, Eth! Posting a question that you don't already know the answer to! Honestly! Go to the back of the class!
It's not my fault my chemistry teacher was a Geordie & I couldn't understand what he was saying [:(]
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if you really want to burn water, i think you can run an electric current through it, leading to it electrolysing into hydrogen and oxygen, in theory in a perfect fuel-oxygen mix to combust into water again, right?
however i am not totally sure, would someone kindly offer a poor GCSE student some advice on this lol
if im right a bottle i put two nails in the bottom of, sealed, and ran a current through for a few weeks a while back should have an explosive gas mix in the top part?
"Turkeys killed my family" - Chip, 02/09/2005, 12:49
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It will evaporate before it catches flame and coz it's wet
- Big T
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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.
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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.
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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
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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.
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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
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Sorry for the double post...
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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
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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!
http://waterpoweredcar.com/BNE_cosmicwatercell_hq.wmv
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!"
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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..