A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. It achieves this by lowering the activation energy, which is the minimum energy required for the reactants to undergo a chemical reaction and form products. By reducing the activation energy, a catalyst allows more reactant molecules to have sufficient energy to react, thus increasing the rate of the reaction.An example of a catalytic reaction is the decomposition of hydrogen peroxide H2O2 into water H2O and oxygen gas O2 . This reaction can be slow at room temperature, but in the presence of a catalyst, such as manganese dioxide MnO2 , the reaction rate increases significantly.2H2O2 aq 2H2O l + O2 g In this reaction, manganese dioxide acts as a catalyst by providing an alternative reaction pathway with a lower activation energy. The catalyst works by adsorbing the hydrogen peroxide molecules onto its surface, which weakens the O-O bond in the hydrogen peroxide. This makes it easier for the bond to break, and the hydrogen peroxide decomposes into water and oxygen gas more quickly. The manganese dioxide is not consumed in the reaction and can be reused multiple times.In summary, a catalyst increases the rate of a chemical reaction by lowering the activation energy, allowing more reactant molecules to have sufficient energy to react. This results in a faster reaction rate and can be observed in the example of hydrogen peroxide decomposition in the presence of manganese dioxide.