Why does a mixture of diet coke and mentos explode?

Basically it is NOT a chemical reaction. As we all know, carbon dioxide gas is present in coke in the form of bubbles( diet coke has more amount of  CO2). Water molecules in the coke form a micelle(tight mesh) like structure around each CO2 bubble.
Since water molecules attract each other, they need some extra energy to expand the bubble and thus the SURFACE TENSION.A mentos consists of gelatin(flubby rubber like eatables and an important component of bubble gums made from boiling bones). So when mentos is dropped in a coke bottle.....
THEY BREAK THE SURFACE TENSION!!!And multiply the CO2 bubble expansion.

Also mentos contains thousands of tiny pits that are perfect for CO2 expansion-CALLED NUCLEATION!!!also what adds to this is that mentos is heavy and drops at the bottom.Therefore, what u see is a soda rain!!

1. At first, gelatin and arabic gum break the surface tension of tight mesh of  water molecules formed around a CO2 molecule. Thus, new bubbles are formed.
2. Most importantly, is the nucleation reaction. the mentos contains thousands od nucleation sites-the sites that are perfect for CO2 expansion.
3. Thus, u add a mentos chewing gum-it goes to the bottom-surface tension breaks-nucleation starts-LAVA ERUPTS!!!!!

QUITE AMAZING!!!!!