Coke Contains Carbon Dioxide

• Among the many ingredients of Coca-Cola and Diet Coke is one specifically designed to give the beverage a fizzy bite. Carbon Dioxide--a clear, odorless gas in its natural state--is compressed by a machine at the bottling plant and injected into every container of Coke or Diet Coke. The addition of this gas gives the drink its fizzy, bubbly properties known as "carbonation," but it can also create violent reactions when exposed to unusual circumstances.
  
  

Carbon Dioxide Causes Reactions

• Under normal conditions, the carbon dioxide in Coke and Diet Coke products remains embedded in the liquid soda while the beverage is inside its pressurized container, then begins slowly turning back into a gas when the can or bottle is opened (this conversion to a gaseous state creates the fizzy sound that can be heard when a soda bottle is opened). If the carbon dioxide is somehow aggravated, though, the process can change. If the soda is shaken before the container is opened, for example, the excited carbon dioxide molecules rapidly expand when depressurized and escape in a messy explosion. If a foreign substance, like Mentos, is introduced into the carbonated beverage, the reaction can be equally explosive.
  
  

Mentos Hasten The Reaction

• When Mentos candies are dropped into a Coke or Diet Coke beverage, the new substance introduced into the carbonated liquid quickly reacts with the embedded carbon dioxide gas. Carbon dioxide tends to attach itself to the surface of solid objects that enter carbonated liquids, and Mentos provide a large, porous surface with many nooks onto which the carbon dioxide molecules can attach. As the candy begins to break down in the Coke or Diet Coke drink, the gummy coating dissolves and erodes the surface tension of the liquid. As the carbon dioxide attaches to the candy and reconverts itself, the escaping gas exploits the reduced surface tension of the beverage to rapidly and explosively exit the container. Because Mentos are heavy and do not float, the process is repeated as the candy falls to the bottom of the beverage container, producing additional force with which the newly released carbon dioxide gas exits the beverage container. The escaping gas carries small amounts of liquid and syrup from the Coke or Diet Coke product along with it, producing the familiar geyser of soda.