Glow sticks are fascinating and a great example for chemiluminescence.
They consist of an elastic plastic tube closed at both ends (1) and a brittle inner container, often made out of glass. Inside the container there is a hydrogen peroxide solution (2), the elastic tube is filled with dyes and diphenyl oxalate (3).
Adapted image, published by Pbroks13 under CC BY 3.0 licence
But why does it start to glow?
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Bending the elastic tube may cause the brittle container to break, releasing hydrogen peroxide and starting the initial reaction. Hydrogen peroxide and diphenyl oxalate mix and the resulting chemical reaction yields 1,2-dioxetanedione and phenol.
Diphenyloxalate.wal (14.9 KB) -
1,2-dioxetanedione is not very stable and spontaneously decomposes to carbon dioxide, releasing lots of energy.
1,2-Dioxetanedion.wal (9.7 KB) -
The energy released excites the dye, meaning that its valence electrons move to higher energy levels. As this is no stable configuration they will “fall” back to their initial energy level releasing a photon. Depending on the dye and the energy difference between the two energy levels the photon will have a certain wavelength, which we can see as a certain color. You may be wondering though, why glow sticks do not get hot with all this energy released. Just like visible light heat is also an electromagnetic wave, but of different wavelength. As mentioned before, only specific wavelengths can be emitted by valance electrons, matching the differences between the electron’s energy levels. For the dyes used these wavelengths are usually somewhere between 400 and 700 nm, which we experience as visible light.
DPA.wal (21.3 KB)