A level Chemistry · Edexcel 9CH0 · Topic 15D
Catalysis
Key points
- Transition metals are good catalysts because they have variable oxidation states and can adsorb reactants on their surface.
- Heterogeneous catalysts are in a different phase: reactants adsorb onto active sites, bonds weaken, products form and desorb. Examples: Fe in the Haber process, V₂O₅ in the Contact process, Pt/Rh/Pd in catalytic converters.
- V₂O₅ works by changing oxidation state: SO₂ + V₂O₅ → SO₃ + V₂O₄, then V₂O₄ + ½O₂ → V₂O₅.
- Catalysts can be poisoned by impurities (e.g. lead in converters) that block active sites.
- Homogeneous catalysts are in the same phase and work through an intermediate. Fe²⁺ catalyses peroxodisulfate + iodide, a reaction that is slow because two negative ions repel.
- Autocatalysis: Mn²⁺ produced in the manganate(VII)–ethanedioate reaction catalyses the reaction, so rate first rises and then falls.
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Transition metals and their compounds are among the most important catalysts in industry and in the body. They provide an alternative route with a lower activation energy in two ways: by holding reactants on a surface, and by switching…
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