Here we see two people making the biggest mentos and coke explosion I have ever seen, or ever hope to see. They actually set it up so one bottle of coke exploding sets the next one off. By why does candy and soda react so violently? Let's have a look.
These are amazing reactions, and the kinds of things that make you want to head for the grocery store and then out to a clear field. We've all seen coke fizz out of the bottle, and the wide bottled tapering down to a thin neck causes the reaction to blow more than if it were in, say, a bowl. But how does anything cause the coke to fizz that violently.
Tonya Coffey, a physicist at Appalachian State University, took a look at the science that caused this reaction. The most familiar analogous reaction is vinegar and baking soda, so initial thoughts were that there was some kind of acid-base chemical reaction going on. PH testing of the coke before and after the reaction showed no change in acidity. Diet coke and caffeine free coke were tested, and did as well as regular coke. Diet Coke even did a little better. Clearly, the reaction had nothing to do with sugar or caffeine. So what was the deal?
It all has to do with nucleation. We've covered nucleation before. Even when a liquid is dying to bubble, it needs little nucleation sites, either from a rough container or from dust and grit, to get the bubbles started. But how do these sites get bubbles started?