# H2O into H fuel, waste is still H2O?

1. Feb 23, 2010

### bobbobwhite

Just don't understand how that could work, if it does. The only way I could understand it is if the amount of H cracked from input H2O is so infinitessimal that the output H2O mass is nearly unchanged and that waste product is effectively still 100% H2O.

Please comment, or send me to the proper forum. Thanks.

2. Feb 23, 2010

### Mech_Engineer

Splitting 1 mol of water through electrolysis gives you 1 mol diatomic hydrogen (H2) and 1/2 mol diatomic oxygen (O2). It takes energy input (electricity) for this reaction to take place.

Burning the above mixture gives you 1 mol of H2O, and heat. What's not to understand?

3. Feb 23, 2010

### bobbobwhite

Per your haughty reply..... how is 1 mol of H2O electrolized, split product H fuel burned off, and waste product still consist of 1 mol of H2O? The heat results from burning the H mols, so you cannot still have 1 mol H2O as waste if the H mols have been removed, per your example. Not physically possible to end where you started if an element is removed and not replaced in kind somewhere along the process line. If the H is gone, it is no longer H2O, but O.

Perhaps you have a perpetual motion device under wraps too?

4. Feb 23, 2010

### Jobrag

You start with water and run an electric current through it, this splits the bond that holds the hydrogen and oxygen atoms together, the hydrogen is collected. When you need energy you burn the hydrogen in air the hydrogen and oxygen atoms combine this reaction gives off heat, simple.

5. Feb 23, 2010

### mgb_phys

The makers statement that the waste is H2O is referring to running the fuel cell (or whatever)
Yes mech_eng says, creating H2 from H20 also gives you O2 (which is hardly waste) running the engine consumes the H2 and O2 (either from the air or from an O2 supply) and creates only water

6. Feb 23, 2010

### Mech_Engineer

I'm not sure what you found haughty, I was simple and to the point if anything...

Anyway I notice a gross error on your part-
Combustion is not a nuclear reaction, so the amount of Hydrogen and Oxygen atoms is constant. The energy results from the exothermic chemical reaction (combustion) which combines Hydrogen and Oxygen into water. Hydrogen is not burned off, it is simply combined into a new molecule (H2O).

I think you've got an intuitive feeling that this process is not spontaneously reversible, which is correct. The number of Hydrogen and Oxygen atoms is constant, so no atoms need to be added, but to reverse the combustion of Hydrogen and Oxygen it is necessary to add energy to the reaction (commonly in the form of electricity for electrolysis).

Some people claim they can get "free energy" by electrolyzing water, and then burning the gases. You're correct that this is not possible, but it isn't because Hydrogen atoms are lost; it is because energy is lost in the form of heat when Hydrogen and Oxygen burn. It will always take as much or more energy to split water into its constituent gases than you get when burning them.

7. Feb 23, 2010

### bobbobwhite

I understand it all somewhat better now as chemical and not physical, as from your replies I now must assume that my former understanding was in error that upon an action a reaction must also occur that produces changed matter due to the alteration or consumption of some or all of the participants in the action. I now assume that I must have been referencing nuclear reaction and transferring those results to others where such reaction is not the case.

8. Feb 23, 2010

### Staff: Mentor

H2 + 1/2 o2 <=> h2o + e

9. Feb 23, 2010

### Topher925

Where does the electron come from?

10. Feb 23, 2010

### Staff: Mentor

It's not an electron, it is energy and it is a victim of a plot by the forum software to make my post harder to read by reducing all the capital letters to lowercase....

11. Feb 24, 2010

### Mech_Engineer

$$H_{2}+\frac{1}{2}O_{2} \Leftrightarrow H_{2}O+E$$

12. Feb 24, 2010

### Topher925

Ohhhhh. I've been reading electrochemistry papers all day so my mind just automatically assumed it was an electron.