Genetically engineered blood protein can be used to split water into oxygen and hydrogen

Physorg.com ^ | Dec 1, 2007 | Imperial College London

[grey_whiskers]

Isn't a spark exciting the molecules, albiet in a very small area?

Usually, yes. A spark might also be a source of free radicals (atomic / molecular species with unpaired electrons, very reactive) which could also begin reaction.

The point is that for most chemical systems, there is an energy barrier to reaction -- it takes a certain amount of kinetic energy present during the collision of two molecules in order to begin reaction. Introducing heat introduces kinetic energy. Once the reaction begins, the energy released by the formation of the new covalent bonds becomes kinetic energy of the water molecule just formed. When this water molecule runs into another H₂2, then the H₂ or O₂ gets a kick, and can has enough energy to react.

This is why the rate of combustion depends on both temperature and the concentration of the reacting molecules.

Cheers!