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Name: Saeed R.
Status: educator
Grade: 6-8
Location: OH
Country: N/A
Date: March 2006

Question:
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.)



Replies:
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".

Vince Calder


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.

Greg Bradburn



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