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Q & A: Is water a fuel?

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Most recent answer: 09/10/2012
Q:
Why can't water replace the petrol as a fuel for vehicle?
- fazure (age 18)
A:
Fuels are sources of "free energy", F The amount of F above the minimum in some environment is the amount of energy available to do large-scale work. A fuel like petrol can release lots of energy when it reacts with oxygen in the atmosphere. So petrol in an O2 atmosphere has lots of extra F. Water doesn't have any. The reason is very simple. Water is hydrogen that already has been burned. So it's not a fuel anymore.

Mike W.

(published on 09/05/2012)

Follow-Up #1: changing water into fuel

Q:
now we are changing water into hydrogen n oxygen and then use it to run bikes n engines.then how can we say that water is not fuel???
- adeel (age 25)
pakistan
A:
In order to change water into fuel, as you say, you need to separate it into hydrogen and oxygen. You need free energy to do that, more free energy than can be extracted from burning the hydrogen an oxygen. So the hydrogen is a fuel, but not the water.

Would you call CO2 a fuel? If you let photosynthesizing plants work on it for a long time, they'll convert it to sugars and other burnable molecules. All the free energy is supplied by sunlight.

Mike W.

(published on 09/10/2012)

Follow-up on this answer.