On Thu, 16 Oct 2003, Randall Clague wrote:
> Yeah. Anyone know how to compute or look up the activation energy?
> That's going to determine whether a fire goes WHOOSH or KABOOM!
Unfortunately, activation energy for a reaction depends very heavily on
what route it takes. Even simple-looking reactions like H2+O2 typically
happen as a chain of several simpler reactions (the intermediate steps are
often quite unstable, involving things like OH or HO2). Sometimes there
are several different routes active simultaneously.
You need to know the details before you have any hope of determining
activation energy, and even then, it's not an easy thing to calculate.
It's not unheard-of for byproducts of later steps to catalyze earlier
ones, i.e. lower their activation energies. (This is why flame holders
are so important in ramjets -- the fuel burns much faster if you
recirculate a bit of half-burned mix into the newly-arriving mix.)
Unless there have been major advances in this area since my chemistry
courses -- which admittedly were a while back :-) -- the only practical
way to determine activation energy for something weird and little-known
like this would be to experiment. (Carefully. On very small quantities.)
Personally, I'm predicting instability gross enough that the experiment
will be both impractical and moot. :-) The only question is whether it
goes "fizz", "fwoosh", or "BANG".
Henry Spencer
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