Water is not a fuel
From Silent Revolution
Topic: Water is not a fuel!
Every few days, some new website pops on on the net, or a new video pops up on YouTube, or some great "invention" pops up in the press, about how someone has created a new way to create fuel from water alone that will power the world. A few claim to burn it directly, but most propose to turn it into hydrogen, burn that in an engine, and then use part of the energy to run the hydrogen creation process. Great idea, except for one thing:
It's nonsense.
First off, what is being discussed is perpetual motion. You start with what you ended up with, and you've taken energy out in the process. This is a violation of the laws of thermodynamics, which in the entire history of modern science, have never proven to be fallable. So, begin by putting your skeptics glasses high on your nose.
To put it in another perspective, what is being proposed is to burn "ash". Water is the "ash" resulting from burning hydrogen and oxygen. What they are proposing is no different than stating that you're going to take some logs, make a fire, and use the fire to run a generator that will turn its ashes back into wood.
The hydrogen bonded to the oxygen in the water has a "bond energy" -- in this case, 492.2148 kJ mol-1. There are also hydrogen bonds, at 23.3 kJ mol-1[1]. This isn't some theoretical concept; it's basic high school chemistry, and readily measured in the lab. To break bonds requires at least as much energy input as the bond contains. To burn hydrogen will give that much energy output. Notice that there's no excess in the process for you to take. Rather, there's only losses -- the energy that you fail to capture.
Bond energies aren't some elusive concept that exist just because some book says they do. Once again, we're back to basic physics. There are four forces in the world -- two weak (Gravity and the Weak force), and two strong (the Strong force and the Electromagnetic force). Picture a piece of metal touching a magnet, drifting through space. Will it ever just fall off on its own? No; of course not. The metal is in a "minimum potential energy state". The magnet draws things together as closely as it can; to move the metal off it, you would have to be putting energy into the system to undo the work that the magnet has already done. By separating the metal and the magnet, there is now potential energy -- the same amount of energy that went into the system through the act of separating them. Let go, and the metal will energetically slam back into the magnet. It's obvious, however, that this energetic release is merely the same amount as the energy that you spent pulling those two apart.
Bond energies work the same way. The hydrogen and oxygen in water "want" to be together, because it's the lowest energy state for them. To get them out of that low energy state means transferring to the water molecule the amount of energy to get them out of that state, enough to counter the forces that, like in the case of the magnet and metal above, are holding them together. And that's the amount of energy the hydrogen and oxygen will get back if they ever were to rejoin, such as in burning the hydrogen.
[edit] Some specific systems
Radio waves and saltwater: You put more energy into making the radio waves than you get out of the hydrogen
Electrolysis: Yes, electrolysis can split water into hydrogen and oxygen. No, you will always spend more energy in electricity than you get out of the combustion of the hydrogen.
Battery in water making it flammable: Don't be dumb and fall for YouTube hoaxes. I would have thought that people would already be familiar with the concept of "camera magic", but you'd be surprised. If you really think you can burn water by dropping a battery into it, go ahead and try it at home.
(Hint: for those who still can't figure it out, they simply replaced the water with alcohol when they cut camera.)
