Question

why the oxygen and hydrogen do not react in air to form water?

Answer 1

You need energy to force the oxygen atom together with the 2 hydrogen atoms! For example, when they launch the space shuttle, the fuel is a combination of liquid hydrogen and liquid oxygen and when they add a flame, the two react, are forced together, and give off their own heat(exothermic reaction) to sustain the cascade of the reaction until the fuel has all been turned into water vapor! That is what the white trails of the shuttle are made of, water vapor. In nature, this reaction rarely happens due to the fact that we have a low percentage of free hydrogen in the atmosphere. It may happen on a small scale with lightning, but nothing to dramatic! Hope this helps!

Answer 2

If you really wanna get technical, we can talk about electron exchange and how eager Oxygen atoms are to combine with other oxygen atoms to make O2 which is what we breath. That is also another reason that the the two don't react spontaneously with each other in the air because a single Oxygen atom is highly unstable and almost always bound with another element like another oxygen to make O2 which is what is floating around along with nitrogen gas and other trace elements to create what we call air! Good luck!

Answer 3

Actually, they do, but not at a noticeable rate. For a reaction to occur, the energy of the reactants' particles must exceed what is known as the activation energy. The shape of the Boltzmann distribution shows that, no matter how small, their is always are chance of some particles having this energy and hence reacting: http://upload.wikimedia.org/wikipedia/commons/thumb/0/01/MaxwellBoltzmann-en.svg/360px-MaxwellBoltzmann-en.svg.png Therefore, every possible reaction is happening everywhere at once, even if the effects are negligible. Changing the conditions doesn't change whether the reaction happens or not, merely it's rate.