Hydrogen peroxide, H2O2, decomposes slowly in aqueous solution according to the overall reaction
2 H2O2(aq) → 2 H2O(l) + O2(g)
A student monitors the rate of decomposition at 25 °C in a 0.500 mol L−1 solution that is free of catalyst. The student will repeat the experiment the next day but wants the decomposition rate to be approximately twice as large while still avoiding the use of any catalyst. The only experimental variables the laboratory protocol allows the student to adjust are (1) the initial concentration of H2O2 and (2) the temperature, which may not exceed 35 °C for safety reasons.
Assume that, under the conditions given, the decomposition rate is first order in [H2O2] and that the activation energy for the uncatalyzed reaction is 76 kJ mol−1.
(a) Describe qualitatively how increasing the initial concentration of H2O2 affects the rate of the reaction at constant temperature.
(b) Describe qualitatively how increasing the temperature affects the rate of the reaction at constant concentration.
(c) The student decides to change only one variable. Identify which single modification—either adjusting [H2O2] or adjusting temperature—would be more effective for reliably attaining a rate that is approximately double the original rate, and justify your choice using kinetic reasoning that references molecular collisions and activation energy.