Question about the energy of hydrogen

[Gerdih]

A flame of hydrogen compensate the energy wasted to produce it?

 

[Artlav]

Uh?
Hydrogen burns with oxygen, releasing energy.
Where is the energy wasted to produce it?

 

[Gerdih]

I mean to get hydrogen

 

[tori]

The energy required to break a molecule of H₂O is equal to the energy released by producing it (burning hydrogen).

The efficiency of both processes is not absolute however. You can e.g. electrolyze water with an efficiency of let's say 20%. Then you burn hydrogen releasing the energy and capture it at say 60% efficiency. So you end up recovering just 12% of it.

edited: wording of the first sentence