May/June 2026 Paper 41

Aqueous hydrogen peroxide, H${}_2$O${}_2$, decomposes to produce water and oxygen gas. Manganese(IV) oxide is a catalyst in this reaction. A student adds powdered manganese(IV) oxide to aqueous hydrogen peroxide in a conical flask as shown in Figure 4.1. The volume in the gas syringe is measured at regular time intervals. The volume increases as time increases.

Write a symbol equation for the decomposition of aqueous hydrogen peroxide. Include state symbols.

State what is meant by the term catalyst.

The rate of reaction is highest at the start of the reaction. The rate of reaction decreases as time increases. The reaction eventually stops. Explain why the rate of reaction is highest at the start of the reaction.

Explain why the reaction stops.

The experiment is repeated at a lower temperature. Explain why the rate of reaction is lower at the lower temperature.