2H2O2 → 2H2O+O2
This process is thermodynamically favorable. It has a ΔHo of −98.2 kJ·mol−1 and a ΔS of 70.5 J·mol−1·K−1. The rate of decomposition is dependent on the temperature (a cool environment slows down decomposition, therefore hydrogen peroxide is often stored in a refrigerator) and on the concentration of the peroxide, as well as the pH and the presence of impurities and stabilizers. Hydrogen peroxide is incompatible with many substances that catalyse its decomposition, including most of the transition metals and their compounds. Common catalysts include manganese dioxide, silver, and platinum. The same reaction is catalysed by the enzyme catalase, found in the liver, whose main function in the body is the removal of toxic byproducts of metabolism and the reduction of oxidative stress. The decomposition occurs more rapidly in alkali, so acid is often added as a stabilizer.
The liberation of oxygen and energy in the decomposition has dangerous side-effects. Spilling high concentrations of hydrogen peroxide on a flammable substance can cause an immediate fire, which is further accelerated by the oxygen released from the decomposing hydrogen peroxide. High test peroxide, or HTP (also called high-strength peroxide) must be stored in a suitable, vented container to prevent the buildup of oxygen gas, which would otherwise lead to the eventual rupture of the container.
In the presence of certain catalysts, such as Fe2+
, the decomposition may take a different path, with free radicals such as HO· (hydroxyl) and HOO· (hydroperoxyl) being formed. A combination of H
2 and Fe2+
is known as Fenton's reagent.
A common concentration for hydrogen peroxide is 20-volume, which means that, when 1 volume of this solution of hydrogen peroxide is decomposed, it produces 20 volumes of oxygen (STP). A 20-volume concentration of hydrogen peroxide is equivalent to 1.761 mol/dm3 (Molar solution) or about 6.08%(w/v).
Source: Wikipedia and youtube.