Does a hydrogen-oxygen mixture require ignition to react?

[SAZAR]

Does mixture of hydrogen and oxygen actually has to be ignited or the reaction occurs even without ignition when some critical H:O proportion is reached?

 

[alxm]

Nope, it doesn't spontaneously react at any concentration.

 

[Borek]

In theory such mixture reacts even at room temperature, albeit very slowly. But I don't have access to any kinetic data, so I have no idea whether the reaction at room temperature is observable or not.

 

[SAZAR]

Which reminds me: if you heat the mixture continuously (starting at room temperature and gradually increasing but not to slow) at what temperature would it ignite?

 

[alxm]

In theory such mixture reacts even at room temperature, albeit very slowly.

In theory, diamonds turn into graphite at room temperature, albeit very slowly

Thank god for slow reaction kinetics - or we'd all instantly die in a ball of flame.

 

[SAZAR]

Actually I think I've found it:

http://en.wikipedia.org/wiki/Hydrogen

"The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C (932 °F)."

That high! ...I would have thought it's much lower. ...No way; that must be wrong. (?)

 

[Borek]

"The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C (932 °F)."

This is only some kind of approximation, as autoignition temperature is surely a function of the mixture composition.

--

 

[alxm]

That high! ...I would have thought it's much lower. ...No way; that must be wrong. (?)

Sounds about right to me.

As Borek said, it changes a bit with composition though.