Many people have asked this question: Why does dropping mentos into a bottle of soda create a reaction? According to information from the mentos website, the reaction occurs because of a simple rule of physics. It is not a chemical reaction. Soda/fizzy drinks contain a certain amount of CO2 (carbon dioxide) dissolved in water in the form of tiny bubbles. This combination of water and CO2 molecules is in a permanently unstable state. When it falls into this liquid, this state is disturbed. The more Mentos that are dropped into the liquid, the more this state is aggravated. The reason for this lies in the surface of a Mentos which looks smooth, but is actually very rough! Within the nooks and crannies of the microscopic rough surface, bubbles form, which are in turn transformed into foam, which then leads to very impressive foam fountains.