The reaction between hydrogen peroxide (H2O2) and manganese dioxide (MnO2) is generally exothermic. When manganese dioxide is added to hydrogen peroxide, it acts as a catalyst and facilitates the decomposition of hydrogen peroxide into water (H2O) and oxygen gas (O2). This decomposition reaction releases heat, making it an exothermic process.
The overall reaction can be represented as follows:
\[ 2 \text{H}_2\text{O}_2 (aq) \rightarrow 2 \text{H}_2\text{O} (l) + \text{O}_2 (g) \]
Due to the heat released during this process, the reaction is considered exothermic.