The Naked Scientists

The Naked Scientists Forum

Author Topic: Why doesn't water burn?  (Read 24394 times)

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
Why doesn't water burn?
« on: 03/12/2005 02:02:26 »
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"!)


 

Offline Solvay_1927

  • Sr. Member
  • ****
  • Posts: 383
    • View Profile
Re: Why doesn't water burn?
« Reply #1 on: 03/12/2005 02:11:46 »
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"?
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
Re: Why doesn't water burn?
« Reply #2 on: 03/12/2005 02:46:03 »
quote:
Anyway, in what way is oxygen "flammable"?


OK, correction - it aids combustion
 

Offline Rokitansky

  • Sr. Member
  • ****
  • Posts: 108
    • View Profile
Re: Why doesn't water burn?
« Reply #3 on: 04/12/2005 19:27:47 »
well, water is already burned :)

It`s derived by burning hidrogen :)
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
Re: Why doesn't water burn?
« Reply #4 on: 05/12/2005 01:31:26 »
quote:
It`s derived by burning hidrogen :)


Is it?
 

Offline ukmicky

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 3011
    • View Profile
    • http://www.space-talk.com/
Re: Why doesn't water burn?
« Reply #5 on: 05/12/2005 03:32:59 »
From the doc. Why doesn't water burn?
________________________________________________


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                                      
« Last Edit: 05/12/2005 04:46:38 by ukmicky »
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
Re: Why doesn't water burn?
« Reply #6 on: 05/12/2005 12:44:46 »
Just a pedantic point - water doesn't burn, it scalds[:o)]
 

Offline Rokitansky

  • Sr. Member
  • ****
  • Posts: 108
    • View Profile
Re: Why doesn't water burn?
« Reply #7 on: 05/12/2005 17:14:42 »
quote:
Originally posted by DoctorBeaver

quote:
It`s derived by burning hidrogen :)


Is it?




Yes. Yes it is .
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
Re: Why doesn't water burn?
« Reply #8 on: 05/12/2005 17:37:53 »
I never knew that. Thank you
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
Re: Why doesn't water burn?
« Reply #9 on: 05/12/2005 17:38:56 »
But if burning hydrogen produces water, why didn't the Hindenberg put itself out?
 

Offline robotjesusbeta

  • Jr. Member
  • **
  • Posts: 27
    • View Profile
Re: Why doesn't water burn?
« Reply #10 on: 05/12/2005 20:03:44 »
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?
 

Offline Rokitansky

  • Sr. Member
  • ****
  • Posts: 108
    • View Profile
Re: Why doesn't water burn?
« Reply #11 on: 05/12/2005 20:04:47 »
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.
 

Offline Rokitansky

  • Sr. Member
  • ****
  • Posts: 108
    • View Profile
Re: Why doesn't water burn?
« Reply #12 on: 05/12/2005 20:57:58 »
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 ... :(
« Last Edit: 05/12/2005 21:03:06 by Rokitansky »
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
Re: Why doesn't water burn?
« Reply #13 on: 06/12/2005 00:10:32 »
Darko - take a deep breath! :D
 

Offline Solvay_1927

  • Sr. Member
  • ****
  • Posts: 383
    • View Profile
Re: Why doesn't water burn?
« Reply #14 on: 06/12/2005 00:48:02 »
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.)
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
Re: Why doesn't water burn?
« Reply #15 on: 06/12/2005 12:53:00 »
quote:
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]
 

another_someone

  • Guest
Re: Why doesn't water burn?
« Reply #16 on: 06/12/2005 20:02:19 »
quote:
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.
 

Offline padfoot89

  • First timers
  • *
  • Posts: 9
    • View Profile
Re: Why doesn't water burn?
« Reply #17 on: 11/12/2005 11:03:21 »
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
 

Offline NewBill

  • Jr. Member
  • **
  • Posts: 43
    • View Profile
Re: Why doesn't water burn?
« Reply #18 on: 11/12/2005 15:46:04 »
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.
 

Offline pyromaster222

  • Jr. Member
  • **
  • Posts: 30
    • View Profile
Re: Why doesn't water burn?
« Reply #19 on: 13/12/2005 19:29:07 »
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.
 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Re: Why doesn't water burn?
« Reply #20 on: 15/12/2005 10:00:30 »
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!
« Last Edit: 15/12/2005 10:07:47 by Soul Surfer »
 

Offline Solvay_1927

  • Sr. Member
  • ****
  • Posts: 383
    • View Profile
Re: Why doesn't water burn?
« Reply #21 on: 17/12/2005 01:43:01 »
quote:
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! ;)
 

Offline Solvay_1927

  • Sr. Member
  • ****
  • Posts: 383
    • View Profile
Re: Why doesn't water burn?
« Reply #22 on: 17/12/2005 22:13:58 »
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...)
« Last Edit: 17/12/2005 22:14:40 by Solvay_1927 »
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
Re: Why doesn't water burn?
« Reply #23 on: 18/12/2005 07:29:41 »
quote:
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  :(
 

Offline Steve Vai

  • Jr. Member
  • **
  • Posts: 30
    • View Profile
Re: Why doesn't water burn?
« Reply #24 on: 21/01/2006 00:07:53 »
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
 

The Naked Scientists Forum

Re: Why doesn't water burn?
« Reply #24 on: 21/01/2006 00:07:53 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length