The science fair category is physical science. The secret behind the famous “popping” of Pop Rocks candy is pressurized carbon dioxide gas (CO2). Each of the tiny little candy pebbles contains a small amount of the gas. Pop Rocks candy works very similarly to the carbonation in soda pop. The candy has tiny bubbles of pressurized carbon dioxide gas trapped inside. So it's not really a chemical reaction as much as a physical release of small amounts of trapped gas. The soda, a carbonated liquid to begin with, contains lots of pressurized C02. Pop Rocks are pressurized with carbon dioxide, creating tiny pockets of bubbles inside the candy. When the soda is at a higher pressure, it can hold more carbon dioxide. When the soda is opened to the
