h2o

[BIGDOGY]

Both hydrogen and oxygen are explosive, but when combined to produce water the resulting mixture is not.
Why?

[figure]

Hot h2o can cause a volatile explosion.

[ChuckFickens]

oxygen's explosive!!! don't anybody light a match please!!!

When something burns it combines with oxygen. Water is the result of hydrogen "burning"... it already combined with oxygen. You really could say that it already burnt and therefore will not burn again.

[gen2]

Hydrogen is not explosive
Oxygen is not explosive

However

A MIXTURE of hydrogen and oxygen IS explosive
The explosion is the release of energy as the atoms combine to form water.

The water is NOT explosive because the energy has already gone. If you put energy back in (in the form of electricity) you can turn the water back into hydrogen and oxygen which you can explode again.

[gen2]

Yes niceboy, Hydrogen powered engines already exist.

[Marg0]

Water powered engines also, in the form to which figure alludes. I think some scottish guy invented it.

Didn't someone just find you can change the properties of water by firing radio waves at it?

[beso]

A water powered engine makes as much sense as a carbon dioxide powered engine. Both are the final products of combustion and there is no practical way of extracting further chemical energy from them.

Any process that changes the properties so that energy can be extracted will require more energy being put in first.