Why does soda shoot up when you add Mentos?

When Mentos are added to soda, a rapid exothermic reaction occurs that results in the release of carbon dioxide gas. This gas causes the soda to erupt out of the container due to the sudden increase in pressure.

The rough surface of the Mentos candies acts as nucleation sites for the formation of carbon dioxide bubbles. These bubbles rapidly grow in size and rise to the surface, causing the soda to fizz. The high concentration of dissolved sugar in soda also contributes to the rapid release of gas, as the sugar molecules act as additional nucleation sites.

In addition, the Mentos contain gelatin, which further increases the surface area available for bubble formation. The combination of these factors leads to the dramatic eruption of soda when Mentos are added.

It's worth noting that not all Mentos candies produce the same effect. Only certain varieties, such as the mint and cola flavours, contain the necessary combination of ingredients and surface texture to cause the eruption.