Why do Mentos and soda create a geyser?

When Mentos are dropped into a bottle of soda, it creates a geyser because of a physical reaction between the candy's surface characteristics and the chemical composition of the soda. Here's a detailed explanation of the process:

1. Nucleation Sites: Mentos candies have a very rough surface with countless tiny pores. These pores act as nucleation sites for carbon dioxide gas bubbles in the soda.

2. Gas Formation: The soda contains dissolved carbon dioxide gas. When Mentos are dropped in, the rough surface of the candy provides nucleation sites for the gas to form bubbles.

3. Rapid Release of Gas: The pores in the Mentos' surface create an ideal environment for the rapid release of carbon dioxide bubbles from the soda. The bubbles form and rise to the surface quickly.

4. Collision and Agitation: As more and more bubbles are formed, they collide with each other and the liquid, creating agitation and turbulence. This agitation causes a buildup of pressure inside the bottle.

5. Eruption: The increasing pressure inside the bottle pushes the soda-bubble mixture upward, creating a geyser effect. The eruption continues until the pressure is released or the soda runs out.

Factors such as the number of Mentos candies, the type of soda (different sodas have varying gas content), the temperature of the soda, and the size of the bottle can affect the intensity and height of the geyser.

It's important to note that the geyser reaction between Mentos and soda is a physical reaction and does not involve chemical changes. It is caused purely by the physical interaction between the candy's surface and the dissolved gas in the soda.