I've seen before chemistry demonstrations where solutions are mixed with one another and subsequently where the resulting product goes through periodic color changes: for example blue to orange and back to blue again. The reaction seems to go on for awhile at a regular period.
My question - can this reaction be considered resonance in the sense that energy is flowing back and forth between two chemical states? In such reactions are there actually two chemical species between the color changes or just energy level/temperature differences?
Answer
A couple of points:
The demo is probably an oscillating chemical reaction, in which the concentration of a given species increases and decreases repeatedly over time. However, the energy of the overall system is dissipating as that is happening - not oscillating.
Resonance, on the other hand, is a (widely misunderstood) concept that applies to a single chemical species and not a bulk reaction mixture. Resonance does not consist of energy flowing back and forth between two chemical states, but rather is meant to represent a single energy state that is a hybrid between two (or more) classical Lewis structures. A double headed arrow between the two classical structures indicates resonance stabilization — mostly resulting from delocalization of electrons relative to the classical structures. The double headed arrow does not indicate oscillation between those two structures.
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