Catalysis. Demonstration of the catalysis of the decomposition of hydrogen peroxide by manganese(V) oxide. Hydrogen peroxide in the burette has been added to a pile of the manganese(V) oxide catalyst. The liquid is seen to be bubbling, this is the oxygen evolved during the decomposition reaction. The other product is water. Manganese(V) oxide is a heterogeneous catalyst: it is in a different phase to the reactant (solid oxide, liquid peroxide). In this case, it is thought that the reactions take place only at the surface of the catalyst. The mean particle size of the catalyst determines its effect, smaller particles have a more powerful catalytic effect.