Behind the Scenes: Coke and Mentos

Why did the Diet Coke create a geyser when the Mentos was added?  There are a couple of reasons.  First Diet Coke like other sodas is carbonated, which means it contains compressed CO2 in the liquid.  The CO2 is what creates the bubbles in your soda and the hissing noise when you open the cap of a bottle.  The noise is created by the CO2 expanding out of the liquid back into a gas.  When you shake up a soda and open it quickly, it bubbles up and can over flow because the CO2 is being released from the liquid.  The reason Diet Coke is the best soda for this experiment is because it has high levels of CO2 compressed in the liquid.  The second reason the geyser is created is through a process call nucleation that takes place on the surface of the Mentos.  Nucleation means that there are wholes into the surface of the Mentos that increasing the surface area.  When the Mentos is dropped into the CO2 rich liquid the CO2 forms a gas in all of the nucleation sites.  This increases the amount of gas that is formed and all this gas rushes out of the bottle in a geyser.