What is the reaction and chemical equation when hydrogen peroxide is added to manganese dioxide?

Manganese dioxide catalyzes the decomposition of hydrogen peroxide.

Hydrogen peroxide, ##"H"_2"O"_2##, decomposes naturally at a very slow rate to form oxygen gas and water.

When manganese dioxide, ##"MnO"_2##, is added to a solution of hydrogen peroxide, the rate of the reaction increases significantly. Manganese dioxide acts as a catalyst for the decomposition of hydrogen peroxide, meaning that it is not consumed in the reaction.

What the manganese dioxide does is it lowers the activation energy of the reaction from approximately ##"75 kJ/mol"## to a little under ##"60 kJ/mol"##.

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.