Why do the Mentos blow up in coke?

When Mentos mints are added to Coca-Cola, they cause a rapid release of carbon dioxide gas from the liquid. This happens because the bumpy surface of the Mentos candies provides nucleation sites for the formation of carbon dioxide bubbles. As the bubbles grow and rise to the surface, they carry with them some of the liquid, creating the characteristic "eruption" of foam and liquid that is associated with this reaction.

The reason why Mentos work so well with Coke is that the combination of the high sugar content and the low pH of the soda creates an ideal environment for the formation of carbon dioxide bubbles. The sugar in Coke acts as a surface active agent, which helps to stabilize the bubbles and prevent them from coalescing. The low pH of Coke also helps to accelerate the release of carbon dioxide from the liquid.

Other candies and objects that have a bumpy surface, such as rock candy or even a straw, can also cause a similar reaction in Coca-Cola. However, Mentos candies seem to work particularly well because they are very dense and have a large number of nucleation sites on their surface. This means that they can produce a large number of bubbles very quickly, which leads to a more dramatic reaction.