There is a classic high school demonstration in which a few drops of the glycerin(CH2OHCHOHCH2OH) are poured on top of a pile of potassium permanganate (KMnO4) powder. At first nothing seems to happen, which of course begs the question: “Sir, what’s supposed to happen?” which in turn begs the cliche-reply, “Good things come to those who are patient.” Then just as the chatter of disinterest begins to break the silence, white smoke appears, and within seconds, a spectacular violet flame erupts, leaving behind a crusty residue and a harsh smell that, in the absence of a fumehood, grates on the throat and lungs.
It is often said that science allows both young and old adults to regain the curiosity of childhood. Good demonstrations lead to numerous questions. Why is the start of the reaction delayed? Why does it start at all without any mixing or heating? Why does the steam appear before the flames? Why is the flame violet? Are there any practical applications of this reaction?
The activation energy, the energy that must be absorbed in order to get the reaction going, is small, which is why it proceeds unaided. But although relatively small. But small does not imply nonexistent, so it still borrows some heat from the air. The appearance of steam before that of flames suggests that this is not a one-step affair. The mechanism probably goes through more than one intermediate.
The equation is just a summary of the overall reaction, giving no hints of what ensued behind the scenes.
14 KMnO4(s) + 4 C3H5(OH)3(l) –>7 K2CO3(s) + 5 CO2(g) + 16 H2O(g) + Mn2O3(s) In the late 1950’s gentlemen named Kenneth B. Wiberg and Klaus A. Saegebarth investigated the mechanisms of permanganate oxidations, in case you want to pursue the matter.
The flame is violet due to the excitation of the electrons of the potassium ion. Delayed Aerial Ignition Devices (DAID), which shoot a stream of flaming ping-pong balls, make use of this reaction when controlled fires are deliberately set from helicopters.