- #1
SAZAR
- 200
- 0
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?
Does a hydrogen-oxygen mixture require ignition to react?
Click For Summary
Discussion Overview
The discussion centers on whether a mixture of hydrogen and oxygen requires ignition to react or if it can react spontaneously under certain conditions. The scope includes theoretical considerations, reaction kinetics, and the conditions under which ignition may occur.
Discussion Character
- Debate/contested
- Conceptual clarification
- Technical explanation
Main Points Raised
- One participant questions if a hydrogen-oxygen mixture must be ignited or if it can react without ignition at a critical proportion of H:O.
- Another participant asserts that the mixture does not spontaneously react at any concentration.
- Some participants propose that the mixture can react at room temperature, albeit very slowly, but express uncertainty about the observability of such a reaction due to lack of kinetic data.
- A participant raises a question about the temperature at which continuous heating would lead to ignition.
- One participant mentions the autoignition temperature of hydrogen in air as being approximately 500 °C, expressing surprise at the high value.
- Another participant suggests that the autoignition temperature is an approximation and likely varies with the composition of the mixture.
- There is a mix of agreement and skepticism regarding the stated autoignition temperature, with some participants finding it plausible while others question its accuracy.
Areas of Agreement / Disagreement
Participants express differing views on whether hydrogen-oxygen mixtures can react without ignition, and there is no consensus on the specifics of the autoignition temperature or its dependence on mixture composition.
Contextual Notes
Participants note limitations in their understanding of reaction kinetics and the conditions affecting ignition, highlighting the need for more data on the observability of reactions at room temperature.
- #2
alxm
Science Advisor
- 1,848
- 9
Nope, it doesn't spontaneously react at any concentration.
- #3
Borek
Mentor
- 29,204
- 4,626
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.
- #4
SAZAR
- 200
- 0
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?
- #5
alxm
Science Advisor
- 1,848
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Borek said:
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.
- #6
SAZAR
- 200
- 0
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. (?)
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. (?)
- #7
Borek
Mentor
- 29,204
- 4,626
SAZAR said:
This is only some kind of approximation, as autoignition temperature is surely a function of the mixture composition.
--
- #8
alxm
Science Advisor
- 1,848
- 9
SAZAR said:
Sounds about right to me.
As Borek said, it changes a bit with composition though.
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