What makes the reaction happen in coke and Mentos?

The reaction between Coca-Cola and Mentos is a classic example of a nucleation reaction, characterized by the rapid nucleation and growth of carbon dioxide gas bubbles. This reaction occurs due to the unique combination of ingredients present in both Coke and Mentos. Here's a step-by-step explanation of what causes the reaction:

1. Surface Roughness: Mentos have a rough and porous surface, which creates nucleation sites for carbon dioxide bubbles. These nucleation sites provide a surface for the dissolved CO2 gas in the Coke to form bubbles and grow.

2. Gum Arabic: Mentos contain a significant amount of gum arabic, which consists of complex polysaccharides. These polysaccharides act as surfactants, reducing the surface tension of the Coke and allowing for easier release of the dissolved carbon dioxide.

3. Sucralose and Aspartame: Coke is artificially sweetened with a blend of sucralose and aspartame. Sucralose has a high density, which increases the overall density of the liquid, while aspartame forms a complex with benzoic acid (also present in Coke) to increase the surface tension. This combination traps the carbon dioxide bubbles within the liquid, leading to a rapid increase in pressure.

4. Hydrolyzed Collagen: Mentos contain gelatin, which is made of hydrolyzed collagen. Gelatin can bind with water molecules and expand rapidly when it comes in contact with the liquid. This expansion further agitates the Coke, causing a stronger release of dissolved carbon dioxide gas.

5. Eruption: As numerous bubbles form and expand rapidly within the Coke, they generate a significant amount of pressure inside the bottle. This pressure eventually exceeds the strength of the surface tension, causing the liquid to erupt from the bottle in a geyser-like fashion.

In summary, the reaction between Coke and Mentos is driven by the presence of nucleation sites on Mentos' surface, the surfactant-like effect of gum arabic, the increased liquid density and surface tension due to artificial sweeteners, the expansion of gelatin, and the overall increase in pressure within the bottle. These factors collectively contribute to the formation and release of carbon dioxide bubbles, resulting in the spectacular eruption that characterizes this exciting chemical demonstration.