Negative Activation Energy
Name: Saeed R.
Date: March 2006
We know that activation energy is the "minimum"
energy for starting a reaction. But for reactions with a negative
activation (minus) energy, what will this concept be like? (I am
not looking for a mathematical solution but the concept.)
The concept of "activation energy" is "borrowed" from
thermodynamics as an analogy. Since it implies "activation" it
cannot be negative. Having said that, some "activation energies",
such as those involved in chain reactions, are very small, so that
once the reaction has started, the reaction continues at a very
fast, even explosive rate. The activation energy model is A MODEL
not intended to provide a comprehensive explanation or description
of chemical kinetics. As such it has its limits (quite restrictive
limits in some cases). What happens so often in chemistry and
physics is we start with a concept intended to be qualitative and
end up placing too much faith on its range and limitations. Such is
the case with "activation energies".
If a positive activation energy keeps a reaction from occurring
until that amount of energy is provided from the environment then a
negative activation energy would imply you could not stop the
reaction from occurring if you tried. The reactants already has
plenty of energy for the reaction so the only way to prevent the
reaction would be to keep the reactants apart.
Click here to return to the Chemistry Archives
Update: June 2012