Transition metals as catalystsAQA A-Level Chemistry: Mind map

Exam questions on Transition metals as catalysts

1. An ammonia plant makes ammonia by the Haber process. A gaseous mixture of nitrogen and hydrogen at 450 °C and 200 atm is passed over a bed of solid iron. The plant manager reports that, whenever the feed gas is contaminated with traces of sulfur compounds, the output of ammonia falls.
   Explain why catalyst poisoning has a cost implication for the plant.2 marks
2. Sulfuric acid is manufactured by the Contact process. Sulfur dioxide and oxygen are passed at 450 °C over vanadium(V) oxide, V₂O₅, which is spread thinly on the surface of inert silica pellets. The reaction is: SO₂(g) + ½O₂(g) ⇌ SO₃(g).
   Write two equations to show how V₂O₅ acts as a catalyst in this reaction.2 marks
3. In aqueous solution, iodide ions react with peroxodisulfate ions: S₂O₈²⁻(aq) + 2I⁻(aq) → 2SO₄²⁻(aq) + I₂(aq). A technician finds that the reaction is very slow when the two solutions are mixed, but speeds up greatly when a few drops of iron(II) sulfate solution are added.
   Explain, with reference to the ions involved, why the uncatalysed reaction is slow.3 marks