How Does This Work?
H2O2 is the scientific name for hydrogen peroxide, which is made up of two hydrogen molecules and two oxygen peroxide. Hydrogen peroxide looks like water (H2O), but the additional oxygen molecule atom results in a powerful oxidizer.
Hydrogen peroxide is thermodynamically unstable, as it decomposes to form water and oxygen. As the rate of decomposition increases, the concentration and pH (the measure of the acidity or basicity of a solution), the cool, and diluted acidic solution stabilize the hydrogen peroxide. The decomposition of hydrogen peroxide creates more oxygen and heat; this can be dangerous because high concentration of hydrogen peroxide on an inflammable substance can cause fire.
The sodium iodide acts as a catalyst, which is a substance that increases the rate of a chemical reaction. It also causes the hydrogen peroxide to decompose into water and oxygen molecules causing oxygen gas (seen occurring above the reaction) and foam.