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Hey Chemists (not you Mr Boots)

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Hey Chemists (not you Mr Boots)

Old 15th Oct 2008, 12:49
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Hey Chemists (not you Mr Boots)

On the basis that there's no such thing as a stupid question, only stupid people asking them:

Why is it so difficult to split water into its constituent atoms?

The resulting gases could then be compressed and exploded in some kind of 'jet engine' and used to fly people about the sky in winged ships. Thus freeing mankind of his addiction to fossil fuels and saving the planet and the foxes and stuff.

I know I should know this. But I don't.
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Old 15th Oct 2008, 12:56
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It's been tried and acheived before - but the results are a teensy bit uncontrollable and result in a rather large mushroom cloud and irradiated bits of the South Pacific.

It requires a large amount of energy expended to break the strong and weak nuclear forces which bind the atomic nuclei together.
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Old 15th Oct 2008, 13:00
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Laws-of-energy
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Old 15th Oct 2008, 13:04
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13thduke asked:
Why is it so difficult to split water into its constituent atoms?
Answer is, that it isn't difficult. It's just that the process of splitting it takes a little more energy than you recover from the recombination. There's a big industry out there trying to shave that margin in order to make it (hydrogen)commercially viable as a fuel.
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Old 15th Oct 2008, 13:48
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Browns Gas,

Brown's Gas
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Old 15th Oct 2008, 13:55
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It's been tried and acheived before - but the results are a teensy bit uncontrollable and result in a rather large mushroom cloud and irradiated bits of the South Pacific.

It requires a large amount of energy expended to break the strong and weak nuclear forces which bind the atomic nuclei together.
Erm... since when has electrolysis resulted in the vapourisation of a tropical paradise? I seem to remember doing this in a test tube in secondary school. Electrolysis that is not the vapourisation of a tropical paradise.
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Old 15th Oct 2008, 14:16
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Browns Gas,

Brown's Gas
At last, a use for our Prime Minister!
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Old 15th Oct 2008, 14:49
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You could always go part way by heating water until it vaporises, but that might have been done before.
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Old 15th Oct 2008, 14:53
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Mr Grimsdale, what has some bint having the sideburns removed from her inner thighs got to do with splitting hydrogen and oxygen?
You say you used to do this at school?
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Old 15th Oct 2008, 15:27
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Yer two main options are either electrolysis as previously described, or some form of catalytic decomposition of water into its constituent elements. Former involves considerable electrical input and crucially is very energy inefficient hence couldn't practically be done in situ on an aeroplane. If you could store hydrogen on board on aircraft in volume (not an easy thing to do) you could do it on the ground beforehand and separate the gases. Of course you wouldn't need to take the oxygen with you since its readily available in the atmosphere, unless you were planning do a VirginGalactic and go sub-orbital.

Many people have tried and failed to find an efficient & low-cost catalyst to break water down (myself included - buggerin' around with exotic metal compounds at uni, thinking I was going to make a fortune and save the planet to boot). Read something recently that the Japanese were making progress in this field, but I wouldn't hold my breath. Again, I doubt if these will ever be efficient enough to be actually be used on board a vehicle with water as the 'store'.
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Old 15th Oct 2008, 15:35
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As an electrochemist I can tell you that you require about 1 kw of electricity to produce about 6 g. of hydrogen and 24 g. of oxygen from the electrolysis of water. You need a different type of chemist (or cleverer one) to tell you how much energy can be obtained from recombining them but I would have thought that it was probably less.
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Old 15th Oct 2008, 19:59
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You use a solar-powered thermocouple to provide the 1.23 electron volts required to split the water molecule, and then it doesn't matter that you get less energy back when you re-combine the constituents, because what you put in hasn't cost you anything, and anything you get back is a bonus.
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Old 15th Oct 2008, 20:28
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I was sufficiently intrigued to do some digging on the 'tinterweb and came across this site:

FlyH2 Aerospace - Hydrogen Powered Aircraft

Uses a hydrogen fuel-cell to power an electrically-powered prop. More efficient & quieter apparently. Mind you, wouldn't like to be in it or near it if the fuel tank ruptured - would make a lovely FAE.
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Old 15th Oct 2008, 20:29
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Water is the exhaust of a hydrogen-oxygen reaction. It's the same thing as capturing the exhaust out of your car and making gasoline out of it. A very complicated and energy expensive problem.

Bluewolf,

Storage is a problem, and the amounts are a problem. If you intend to run your mower now and then it might work. Commuting to work forget it.
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Old 15th Oct 2008, 20:38
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I'm convinced that water is the cheap fuel of the future. It just needs some one to discover the catalyst that splits it economically into hydrogen and water. The best thing though when it is discoverd, is the fact that the arabs don't have much water.....
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Old 15th Oct 2008, 22:24
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Storage is a problem, and the amounts are a problem. If you intend to run your mower now and then it might work. Commuting to work forget it.
Good job there's no shortage of oil then, eh

or how about....your solar electrolysis unit quietly percolates away through the day, filling the metal hydride cell, or the big bladder of go-bang gas, or whatever, and then at night, you burn it in your co-generation unit, and it heats the house and the bathwater and charges your electric car at the same time.
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Old 15th Oct 2008, 22:33
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or you could add certain organic materials to the water which will turn it into beer and then sit and drink the beer while someone else works it out for you.
gets my vote.
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Old 15th Oct 2008, 23:21
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or you could add certain organic materials to the water which will turn it into beer
Or ferment and distil into . . .
. . . pure alcohol (ethanol) . . .

which can be used directly as fuel, Shirley?

from 1908 onward Ford Model T automobiles could be adapted to run on ethanol
More at:- http://tonto.eia.doe.gov/FTPROOT/features/biomass.pdf
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Old 15th Oct 2008, 23:31
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You can do it very easily, but you still need an energy source to distill the ethanol out of the ferment. On top of that there isn't as much potential energy per unit volume of ethanol as there is in gasoline, so you don't get the same m.p.g, so you have to burn more of it...

In Brazil, they burn the spent sugarcane stalks to provide the heat source for distillation, which makes the equation more attractive, but burning sugarcane stalks produces (gasp) CO2....as does burning ethanol or gasoline of course...
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Old 16th Oct 2008, 00:28
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In the 1980s, Denmark generated hot water at plants located near settlements by burning the straw from cereal production (OK they had to collect it and transport it - short distances - but it was otherwise waste material).
This hot water was then piped through heavily insulated pipes to dwellings where it was metered according to temperature drop and volume 'consumed' to provide domestic heating and hot water.
I realise this isn't feasible for vehicular use (AFAIK), but it did generate energy from otherwise 'free' fuel . . .
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