How much energy, say joules, is required to separate the hydrogen atoms from a water molecule?

Question

Several people or companies have claimed to have invented a device that separates hydrogen from water and then uses the hydrogen to power vehicles.

Answer 1

The process is called electrolysis, and it is not a crazy "claim", it is real.

Separating hydrogen gas from water is how certain companies produce small quatities of extremely pure hydrogen. The only controversy is the amount of energy needed to do this is rather large (on the order of 230 kJ per mole of gas). So to power every car in America on hydrogen would require massive amounts of electricity. This is not feasible until renewable energy can be generated in sufficient quantities.

Answer 2

The amount of energy needed to separate hydrogen and water, is just a little higher than the energy you get by combining them (that is burning hydrogen with oxygen).

This should be obvious with a little reflection. Combine the molecules with burning, energy comes out. Put that same energy back in (with a little extra for inevitable loss) and the molecules come apart.

Although I cannot find my source for this my memory is that the energy of combustion of hydrogen is around 60,000 btu/lb

In any discussion about water as fuel, the actual energy is irrelevant, the fact that you are merely transfering the electrical energy into hydrogen as STORAGE (and losing energy as you go) is what needs to be remembered.

Answer 3

75 virgins