Manganese dioxide catalyzes the decomposition of hydrogen peroxide.
When manganese dioxide,
What the manganese dioxide does is it lowers the activation energy of the reaction from approximately
This allows more molecules of hydrogen peroxide to undergo decomposition in a shorter period of time. The balanced chemical equation for this reaction looks like this
#2"H"_ 2"O"_ (2(aq)) stackrel(color(white)(acolor(black)("MnO"_ (2(s)))aaa))(->) 2"H"_ 2"O"_ ((l)) + "O"_(2(g))# #uarr#
Manganese dioxide is written above the arrow (you'll sometimes see it written uder the arrow) because it is not being consumed in the reaction.