Does a hydrogen-oxygen mixture require ignition to react?

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SAZAR
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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?
 

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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.
 
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?
 
Borek said:
In theory such mixture reacts even at room temperature, albeit very slowly.

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

Thank god for slow reaction kinetics - or we'd all instantly die in a ball of flame.
 
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. (?)
 
SAZAR said:
"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.

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SAZAR said:
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.