Water has plenty of oxygen in it. Why doesn't water support combustion?

Answer 1

First, the proportion of water molecules are much, much greater than the oxygen present.

Second, the oxygen present in water are solvated. They are trapped, in their ion form, within 'cages' of water molecules. Thus water does not support combustion.

AH..I thought you were referring to dissolved Oxygen instead of Oxygen atoms present in water molecules. -_- In water molecules, as mentioned above, the oxygen atoms is strongly bonded by covalent bonds to the Hydrogen atoms. As such, even when heated, water will only undergo a change of phase. Properties of a compound is different from its constituting elements.

Answer 2

Because combustion is burning something in Oxygen. So for combustion to take place you have to break both O-H bonds to get free oxygen. This takes a huge amount of energy. The formation of water results from the reaction between Hydrogen and Oxygen. This is an exothermic reaction and therefore H2O is much more stable than H and O seperately.

Answer 3

Because the oxygen has already been reduced when it reacted to form water. Oxygen which supports combustion is O2. Once it has reacted to form a compound, the oxygen is in a different form and can no longer support combustion.