Lighted Sign
Is light absorbtion a sign of a chemical reaction?
I know that emission of light, emission of heat and absortion of heat are all signs, but how about light absorbtion?
No. Absorption of light by a chemical compound is the sign that the light absorbed is of precisely the correct amount of energy (quantum) to excite a chemical bond to a higher energy, or to pump electrons into a higher orbital. That is the whole principle behind things like UV-Vis and IR spectroscopy.
That said, there are some reactions that _are_ photo-catalyzed: the rate of the reaction is dramatically increased upon exposure to certain frequencies of the electromagnetic spectrum.
So, absorption of light MAY be a sign of a chemical reaction occurring, but it is not necessary for a chemical reaction.
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