The Catalytic Decomposition of Hydrogen Peroxide

Chemical Concepts Demonstrated

• Chemisty of hydrogen peroxide
• Disproportation reactions
• Enzyme catalysis

Demonstration

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.

Observations

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.

Contributors

• Dr. George Bodner (Perdue University)