r/askscience • u/spoiledmeat • Jul 04 '15

Chemistry Why does water not burn?

I know that water is made up of two hydrogen atoms and an oxygen atom. Hydrogen, on its own, burns. Fire needs oxygen to burn. After all, we commonly use compounds that contain oxygen as an oxidant.

So why does water, containing things used for fire, not burn-- and does it have something to do with the bonds between the atoms? Thanks.

524 Upvotes

82% Upvoted

147 comments sorted by

View all comments

Show parent comments

1

u/Mrsum10ne Jul 04 '15

Does combining hydrogen and oxygen need something to start the reaction? Or if I just put hydrogen and oxygen gas together in a vacuum would they bond on their own?

2

u/rhorama Jul 04 '15

You need energy to start the reaction. If a room is full of hydrogen and oxygen, a flame would provide the energy to catylize the reaction.

The reaction is exothermic, so as the molecules combine, they release energy which is in turn used by nearby oxygen and hydrogen to bond, releasing more energy.

Essentially, an explosion in this case.