To calculate the reaction rate, we need to know the change in concentration of the reactant hydrogen peroxide over time. The balanced equation for the decomposition of hydrogen peroxide is:2 H2O2 2 H2O + O2Since 2 moles of hydrogen peroxide decompose within 20 seconds, we can calculate the average reaction rate as follows:Reaction rate = Change in concentration of H2O2 / Change in time Reaction rate = Final concentration - Initial concentration / Final time - Initial time In this case, the initial concentration of hydrogen peroxide is 2 moles, and the final concentration is 0 moles since it completely decomposes . The initial time is 0 seconds, and the final time is 20 seconds.Reaction rate = 0 - 2 / 20 - 0 Reaction rate = -2 / 20Reaction rate = -0.1 M/sThe negative sign indicates that the concentration of hydrogen peroxide is decreasing over time. Therefore, the reaction rate of the decomposition of hydrogen peroxide in the presence of a catalyst at 25C and 1 atm pressure is 0.1 M/s.