Catalytic decomposition of ozone in the upper atmosphere can be represented overall…
CHEMISTRY · Multi-part · A Level · Chemistry · Introduction to organic chemistry · Introduction to organic chemistry
Problem
Catalytic decomposition of ozone in the upper atmosphere can be represented overall as 2 O₃(g) → 3 O₂(g).
One proposed sequence of elementary steps occurring on the surface of a dust particle is shown below (all species are in the gas phase).
Step 1 O₂ + O ⇌ O₃ (fast, reaches equilibrium)
Step 2 O₃ + O → 2 O₂ (slow, rate-limiting)
Answer the following questions about this mechanism.
(a) Identify all reaction intermediates in the mechanism and justify your selections based on their role in the sequence of elementary steps.
(b) For the rate law that would be observed for the overall reaction, which of the species O₂, O₃, and O should not appear, and why?
(c) Write an expression for the rate of formation of O₂ in terms of the concentration(s) of only those species present in the reaction mixture before the slow step begins.
State the proportionality (e.g., rate ∝ …) rather than a full algebraic derivation.
(d) Predict qualitatively how the observed rate would change, if at all, when the initial concentration of O₂ is doubled while the concentration of atomic oxygen is held constant at its initial value. Provide reasoning that connects the mechanism to the predicted change.