19.6 The Catalytic Decomposition of Hydrogen Peroxide

Chemical Concepts Demonstrated: Chemisty of hydrogen peroxide, disproportation reactions, enzyme catalysis


  • A slice of potato or liver, drops of catalase enzyme (or prick your finger and use your own blood), a small quantity of MnO2, a clean nail and a rusty nail are all added to different crystallizing dishes containing 30% H2O2.


    The various items foam in the dishes.

Explanation (including important chemical equations):

    Hydrogen peroxide undergoes disproportionation. Both oxidation and reduction occur at the same time.

    2 H2O2 (aq) ---> 2 H2O (l) + O2 (g)        enthalpy: -196.1 kJ/mol

    The activation energy of the reaction is about 75 kJ/mol in the absence of catalyst.   Platinum metal catalysts can lower the activation energy to about 49 kJ/mol.  The catalase enzyme (found in blood) lowers the activation energy to below 8 kJ/mol, which corresponds to an increase in the rate of reaction at physiologial temperatures by a factor of 2 x 10 11 or more.