Question

The label on a bottle of 3% (by volume) hydrogen peroxide, H₂O₂ , purchased at a grocery store, states that the solution should be stored in a cool, dark place. H₂O₂ decomposes slowly over time, and the rate of decomposition increases with an increase in temperature and in the presence of light. However, the rate of decomposition increases dramatically if a small amount of powdered MnO₂ is added to the solution. The decomposition products are H₂O and O₂. MnO₂ is not consumed in the reaction.

(b) What role does MnO₂ play?

Answer 1

MnO2 acts as a catalyst in the decomposition of hydrogen peroxide, speeding up the reaction by providing a lower energy pathway without being consumed.

Step-by-step explanation:

The role that MnO2 plays when added to an aqueous solution of hydrogen peroxide (H2O2) is that of a catalyst. A catalyst is a substance that significantly increases the rate of decomposition of H2O2 without being consumed in the reaction itself.

When hydrogen peroxide decomposes, it forms water and oxygen gas, but this reaction is naturally slow. The presence of MnO2 causes the hydrogen peroxide to decompose rapidly, releasing oxygen and resulting in the production of water.

In a reaction, the catalyst is not counted as either a reactant or a product, hence it is listed above the yield arrow in the equation. MnO2 serves precisely this function in the decomposition of hydrogen peroxide, where it dramatically speeds up the reaction while remaining unchanged at the end of the process.