Hydrogen gas reacts with iodine monochloride according to the overall equation
2 ICl(g) + H2(g) → 2 HCl(g) + I2(g).
A researcher proposes the following *single* elementary step for the reaction:
ICl(g) + ICl(g) + H2(g) → I2(g) + 2 HCl(g) (step X)
The reaction is carried out at 298 K and 1.00 atm total pressure, with all gases initially present at 0.10 M concentration.
Respond to the tasks below.
(a) Using collision-based reasoning, explain why step X is unlikely to be the first elementary step under the stated conditions.
(b) Propose a two-step mechanism that accomplishes the same overall transformation without requiring a termolecular collision. Clearly write each elementary step and identify its molecularity.
(c) For each step in your mechanism from part (b), explain how the molecularity you assigned is consistent with the generally observed frequency of gas-phase collisions at 298 K and 1 atm.