[Phys-l] electrons +- redox +- flame

[John Denker <jsd@av8n.com>]

On 04/12/2012 08:51 PM, Jeff Bigler wrote:

>  I believe this must occur because the
> flame is a redox reaction, and the reaction components were acting as a
> source and/or sink for the electrons arcing between the electrodes of
> the induction coil.

A couple of points, tangential to the original question:

1) In a quite profound sense, there is no such thing as a "source"
 or "sink" of electrons.  Conservation of charge forbids it.
 Conservation of lepton number forbids it.

On 04/13/2012 06:57 AM, Paul Nord wrote:

> > Am I understanding correctly that the spark appears to jump to 
> > the flame and terminate there?

That is very unlikely to occur with a typical-sized flame,
because the capacitance of the flame is too small ... although 
on a larger size-scale, an analogous thing can happen, as we 
see demonstrated here:
  http://www.youtube.com/watch?v=9tzga6qAaBA#t=0m55s

This is a 100% flagrant violation of Kirchhoff's so-called
"laws", but it can be understood in terms of capacitance,
as discussed here:
  https://carnot.physics.buffalo.edu/archives/2010/7_2010/msg00023.html

=========================

2) We ought to be careful about saying "the flame is a redox
 reaction".

 The term "redox reaction" means "electron transfer reaction".
 The etymology of this term is weird and confusing, but the
 modern meaning is well-established.  The related term 
 "oxidation" is ambiguous and is the source of endless
 confusion.

 In particular, the reaction
          C + O2 --> CO2
 (as written) is generally considered to be /not/ an electron
 transfer reaction, i.e. not a redox reaction, even though it
 involves oxygen.  On the other side of the same coin, the
 reaction of hydrochloric acid with zinc is considered a
 redox reaction, even though it does not involve oxygen.

 To be sure, there are some ions in the flame, as the spark-
 coil experiment demonstrates, but this is a relatively minor
 component.  As I understand it (and I'm not an expert), this
 is mostly because the flame is hot, not because there is 
 any particular fancy redox chemistry going on.  Mostly, the 
 reaction pathway involves uncharged free radicals.  

 Also: most of  the light from the visible flame comes from 
 quasi-black-body radiation from smallish hot particles (the 
 same particles that produce soot if they don't get burned 
 up) ... so the flame is not in the same category as a neon
 sign, which entirely depends on light emitted by ions.

 On the other hand, in non-flame situations, you can arrange
 similar reactions that do proceed via redox pathways, as in
 an electrochemical fuel cell.  Still, my point remains that 
 we need to be careful about assuming every reaction that 
 consumes fuel is a "redox" reaction, because in a fuel cell
 it takes a lot of tricky engineering to promote the redox 
 pathway and shut down competing pathways.
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