I read an article the other day on new and renewable fuel sources. After reading it, I decided to put my head to use and see if I could come up with something better…WATER!..And now the question: Why doesn’t water burn? I mean considering that it is a compound made up of a fuel(H), and an oxygent (O), it seems that it would be the perfect fuel source. What’s puzzling is that in reality, H2O is the opposite of this. It not only puts out fires, it is one of the most indistuctable substances on earth. How can such a seemingly volatile mixure be useless as fuel?
Everything burns just fine. You just need enough heat to get it going. Granite, steel and concrete burn nicely in a nuclear explosion.
What you are probably referring to is the separation of water into its elemental components, namely, oxygen and hydrogen. This is commonly performed through a process called electrolysis. Electrical current is used to disassociate water and two very flammable gases are the result.
This has been covered before, but it’s quicker to explain that look up the original thread(s).
If you have some hydrogen gas, and a spark to ignite it, it will burn (and very well, too, ever seen the film of the Hindenburg?). As it does, it combines with the oxygen in the air to form water. Water doesn’t burn because it’s the residue from something that’s already burned.
You can seperate water into hydrogen and oxygen by placing two electrodes in water and applying a current. It takes electrical energy to seperate them, and if you burn the hydrogen again you get the energy back as heat and light.
In addition to being covered on this board before, Cecil has already answered the question:
http://www.straightdope.com/columns/970905.html
Arjuna34
In the future our energy needs will be filled by vast floating islands of solar cells electrolyzing sea water into hydrogen, which will be compressed, cooled to a liquid, and shipped in huge tankers to fuel depots. The oxygen will be released into the atmosphere. Cars will either burn the hydrogen in turbines, internal combustion engines, or fuel cells. Enterprising individuals will be able to fulfill their home heating and lighting needs by setting up electrolysis systems on their roofs. It will be the end of the oil companies, the electrical company, and the gas company, and the oil sheiks. Can you guess why we aren’t doing it now?
It will also mean the end of air pollution, energy shortages, gas lines, mideast diplomacy, and dependence upon large corporations.
Solar cells are made of sand. The energy will be provided by the sun. The raw materials cover 7/10 of the earth. No one will get rich off of this (we’ll be holding bake sales for the Rockefellers and the Bushes), which is why it must be government funded.
I’m not sure I agree with you this, gab. It sounds like the companies that make the vast floating islands, huge tankers and fuel cells will make out like bandits.
If you drop lithium into water, the lithium will burst into flames. Is that close enough?
(BTW, I thought electrolysis was something else entirely)
Separating water into hydrogen and oxygen takes more energy than you get by subquently burning the hydrogen (either via fuel cell or combustion engine, etc.). Recall that burning hydrogen results in water, the thing you’d started with. I think you’ve found the perfect fuel for a perpetual motion machine 
Arjuna34
I don’t know about lithium, but sodium and potassium are loads of fun.
Arjuna is right. If you had a PV system on your roof, why would you make Hydrogen and Oxygen? Run the power through an inverter and use the energy directly. At $2000 per kW, it could pay for it self in just a little over… Wait, my calcs show that if you use any reasonable cost of capital it never pays for itself, and in fact costs at least double what buying power from the local utility costs. Damn! Oh well, back to the drawing board.
We had people selling electrolosis devices to businesses to convert water into a cheap replacement for natural gas. It works as long as you don’t take the cost of electricity into account, and you pay to seriously modify any natural gas burning equipment. If you do take the electrical cost into account it is only about 8 times as expensive as the gas.
Electrolosys and subsequent hydrogen burning provides a means to store and transport energy, but not to generate it. It may be that someday, solar cells will be efficient enough to make what gabbyhayes suggests practical. Unfortunately, that day has not yet come. It costs more energy to make a solar cell than it does to make a battery which will last just as long. The only place where solar cells currently have a practical application is situations where a battery would be too heavy or bulky, such as satellites or some calculators.
That is sheer idiocy. You don’t “use up” a solar cell. As long as it’s exposed to light, it generates an electrical current–today, tomorrow, next week, and in the year 2010. Once the cell is made, it creates an unlimited amount of electricty from light. This doesn’t violate the conservation of energy–the sunlight is the source of energy. It knocks electrons off the doped silicon and in quantity, they are electrical current. It’s true that cells are not very efficient yet, but there is no size limit to an installation in the South Pacific. You could create a solar array the size of south america and still take up only a small fraction of the surface. Furthermore, solar cells are only one of several options available for turning solar energy into electricity. You could have a series of parabolic mirrors focusing the solar heat on a collector where distilled water is boiled and used to turn a turbine or–even more into the realm of science fiction–you could use the heat differential of surface water versus deep water to generate a flow of a more volatile fluid which could turn turbines. There are people in remote areas today who generate all of their needed energy with solar cells, including hydrogen for heat and refrigeration.
… and we have a total collapse of the biosphere, as the floating artificial islands block just enough sunlight to impact the phytoplankton of the oceans, and the remaining life in the surface waters of the Earth is electrocuted. All it would take is that one last ten-square-mile photovoltaic cell in a tropical sea. (The tropical seas would be covered first to take advantage of the more direct sunlight.) …
Somehow the biosphere survived the emergence of the continents. The electrical potential is only between the electrodes which might be inches apart. During global warming, excessive heat of the south pacific results in disastrous consequences that might be ameliorated by an alternative form of absorption–e.g. shade from photovoltaic cells. Plankton is most abundant at the poles, which is why baleen whales go there to feed.
Hey, I like this! Do you think we can block enough sun to inhibit oxygen production and return the planet to it’s rightful owners, cruelly burned alive 3+ billion years ago?
Once burned, twice shy. Fool me once, shame on you. Fool me for three and a half billion years, shame on me.
In fact, the process of turning seawater into hydrogen would much more efficiently convert sunlight and water into oxygen than photosynthesis. I can hear the grumbling in the background, so let me rush to explain: When a plant turns sunlight, air, and water into sugars and oxygen, it has a limited lifespan and will eventually die, sink, and rot, which takes back a certain percentage of the original oxygen. Also, at night, plants absorb oxygen. Solar cells, even if they are destroyed or thrown away because they are obsolete remain completely stable silicon crystals, so they don’t take up any oxygen. If the system were 100% efficient, all of the oxygen created would be taken up in the eventual burning of the hydrogen–BUT not all of the hydrogen will burn, leaving a net plus in oxygen. Furthermore, the hydrogen, once it is hugely abundant, may be used for other purposes than fuel. For example, it could be used as insulation (the r factor of a wall of hydrogen would be only a little lower than a wall containing a vacuum) or dry cleaning. Liquid hydrogen would be almost superfluid. Mixed with a small amount of detergent, it would clean fabric almost perfectly. When the cleaning is done, it could be vented away safely without residue.