A student is studying the thermal decomposition reaction
2 H₂O₂(aq) → 2 H₂O(l) + O₂(g)
in two separate trials carried out at the same temperature and concentrations: one trial includes a small amount of MnO₂ powder, and the other does not. The student makes the following qualitative observations:
• The appearance of bubbles (O₂ gas) occurs sooner and at a noticeably faster rate in the trial containing MnO₂.
• At the end of both trials, the same total volume of O₂ has formed, and the MnO₂ can be filtered out unchanged.
Use these observations to address the questions below.
(a) Explain, in terms of the energy profile for the reaction, why the presence of MnO₂ changes the observed rate of O₂ production without altering the total amount of O₂ formed.
(b) Using particulate-level reasoning, justify why MnO₂ does not appear in the balanced overall equation even though it participates in the reaction mechanism.
(c) Distinguish among a reactant, a catalyst, and an inhibitor by describing one characteristic experimental observation that would allow you to identify each role in a reaction mixture.