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Posted by matthew on March 5, 2008, 10:36 am
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I have always been puzzled by the way that acetylene produces a higher
flame temperature than propane or natural gas, even though it's total
heat output is lower. Also, I have never been able to understand the
nature of the explosive reaction that can occur when acetylene exceeds
15 psi. This reaction is evidently able to occur without oxygen. I
know a little bit about about chemistry, and from what I understand,
it seems to me that the triple carbon bond in the acetylene molecule
would make it more stable, rather than less, as it seems to be. Does
anyone out there have a good explanation of why acetylene behaves the
way it does? Thanks much!
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Posted by David Billington on March 5, 2008, 2:01 pm
Please log in for more thread options matthew wrote:
> I have always been puzzled by the way that acetylene produces a higher
> flame temperature than propane or natural gas, even though it's total
> heat output is lower. Also, I have never been able to understand the
> nature of the explosive reaction that can occur when acetylene exceeds
> 15 psi. This reaction is evidently able to occur without oxygen. I
> know a little bit about about chemistry, and from what I understand,
> it seems to me that the triple carbon bond in the acetylene molecule
> would make it more stable, rather than less, as it seems to be. Does
> anyone out there have a good explanation of why acetylene behaves the
> way it does? Thanks much!
>
>
I can't help a great deal as I am not a chemist but I did pose this sort
of question to one of my chemistry teachers and he thought the issue of
the instability was due to the 'stress' the triple bonds joining the
carbon atoms were under. basically they are not at the angles they would
like to be at but rather sort of forced and so likely to break easily.
I had been meaning to ask a similar question, I have always been told
that acetylene is likely to spontaneously decompose above about 30 psi
so why doesn't it do so when a new bottle registers 250psi on the gauge.
I am aware of the dissolving in acetone but I presume at some point
within the regulator gaseous acetylene is present at a high pressure to
be regulated down.
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Posted by matthew on March 5, 2008, 2:08 pm
Please log in for more thread options Thanks for the reply!
On Mar 5, 1:01=A0pm, David Billington
> I had been meaning to ask a similar question, I have always been told
> that acetylene is likely to spontaneously decompose above about 30 psi
> so why doesn't it do so when a new bottle registers 250psi on the gauge.
> I am aware of the dissolving in acetone but I presume at some point
> within the regulator =A0gaseous acetylene is present at a high pressure to=
> be regulated down.
Yes, I have also been curious about that same question.
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Posted by Grant Erwin on March 5, 2008, 4:36 pm
Please log in for more thread options matthew wrote:
> Thanks for the reply!
>
> On Mar 5, 1:01 pm, David Billington
>
>>I had been meaning to ask a similar question, I have always been told
>>that acetylene is likely to spontaneously decompose above about 30 psi
>>so why doesn't it do so when a new bottle registers 250psi on the gauge.
>>I am aware of the dissolving in acetone but I presume at some point
>>within the regulator gaseous acetylene is present at a high pressure to
>>be regulated down.
>
>
> Yes, I have also been curious about that same question.
Maybe it's because there's no oxygen inside there to react with?
Grant Erwin
Kirkland, Washington
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Posted by Leo Lichtman on March 5, 2008, 5:22 pm
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"Grant Erwin" wrote: Maybe it's because there's no oxygen inside there to
react with?
^^^^^^^^^^^^^^^^
I understand that acetylene becomes unstable and dangerous at pressures
above 15PSI, which is why they dissolve it in pulpy liquid mix inside the
cylinder. There is no oxygen there, so that can't explain it. Why it
doesn't explode in the space at the top of the cylinder, in the regulator
neck, etc., is probably due to the very small volume. Possibly it's a heat
transfer question--small passages have a larger relative area to get rid of
heat, reducing the temperature rise from any reaction that tries to start.
If the temperature doesn't go up, the reaction rate doesn't go up.
I believe the explanation for the instability of the triple bond that David
B. gave is correct. Chemists draw the carbon atom as a "C", with bonds
going "north, south, east and west." This is not a true representation of
the atom, but it will do for discussion. In order to form a triple bond,
the bonds have to move from their relaxed position to join similar bonds on
the other carbon atom, so they are stretched out of shape, and therefore
more easily broken.
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> flame temperature than propane or natural gas, even though it's total
> heat output is lower. Also, I have never been able to understand the
> nature of the explosive reaction that can occur when acetylene exceeds
> 15 psi. This reaction is evidently able to occur without oxygen. I
> know a little bit about about chemistry, and from what I understand,
> it seems to me that the triple carbon bond in the acetylene molecule
> would make it more stable, rather than less, as it seems to be. Does
> anyone out there have a good explanation of why acetylene behaves the
> way it does? Thanks much!
>
>