Lesson 15B.3

15B.3 Transition metals as catalysts Quiz: Pearson Edexcel Chemistry, Unit 15

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 15B.3, Transition metals as catalysts: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 15: Transition Metals, written with Revision Ninja.

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The 20 questions

  1. What is a heterogeneous catalyst?

    • A catalyst in the same phase as the reactants, which mixes fully and reacts through intermediates
    • A catalyst in a different phase from the reactants, with the reaction occurring at its surface
    • A catalyst that raises the activation energy of the reaction and so slows the reaction down
    • A catalyst that is used up in the reaction and must be replaced continuously during the process

  2. What is a homogeneous catalyst?

    • A catalyst that is fully consumed in the reaction
    • A catalyst in a different phase, reacting only at its surface
    • A catalyst in the same phase as the reactants
    • A catalyst that works only at very high pressure

  3. What effect does a catalyst have on the activation energy?

    • It provides an alternative route of lower activation energy, without being used up
    • It shifts the equilibrium position towards the products, which increases the yield at equilibrium
    • It raises the activation energy so that the reaction is slower and the products form less readily
    • It changes the enthalpy change of the reaction, making the products more stable than before

  4. Which catalyst is used in the contact process for converting SO2 to SO3?

    • Iron(II) oxide, which is used in the Haber process rather than in the contact process
    • Vanadium(V) oxide, V2O5
    • Nickel metal, which is used as a hydrogenation catalyst in the manufacture of margarine
    • Vanadium(II) oxide, a reducing agent that would reduce SO2 rather than oxidise it

  5. What is the first step in the mechanism of a catalytic converter?

    • Diffusion of N2 out of the engine into the air, which removes the nitrogen before any reaction
    • Adsorption of CO and NO molecules onto the surface of the catalyst
    • Desorption of CO2 from the gas phase, which occurs before any molecules reach the catalyst
    • Reaction of CO with the exhaust pipe walls, which are made of a catalytic transition metal

  6. What role does Mn2+ play in the reaction between MnO4- and C2O4 2-?

    • It is an autocatalyst, produced by the reaction and speeding it up as it forms
    • It has no effect on the rate of the reaction, because only the oxalate ion determines its speed
    • It slows the reaction by removing oxalate ions from the solution as an insoluble precipitate
    • It is the oxidant that is consumed in the first step, so its concentration falls steadily

  7. What role does Fe2+ play in catalysing the reaction between I- and S2O8 2-?

    • It is consumed and never regenerated, so a large amount must be added at the start
    • It slows the reaction by precipitating iodide ions as an insoluble iron salt in the flask
    • It acts as a homogeneous catalyst, cycling between Fe2+ and Fe3+ states
    • It is the oxidant, consumed in the first step, which is then regenerated later in the reaction

  8. Which catalyst is used in the Haber process for ammonia synthesis?

    • Nickel metal
    • Vanadium(V) oxide
    • Platinum-rhodium gauze
    • Iron, with promoters

  9. Which catalyst is used in the Ostwald process for oxidising ammonia?

    • Manganese(IV) oxide, which catalyses hydrogen peroxide decomposition but is not used in the contact process
    • Vanadium(V) oxide, which is the catalyst used in the contact process for sulfuric acid
    • Copper(I) oxide, which is used as a catalyst in methanol synthesis at high pressure
    • Platinum-rhodium gauze

  10. Why are platinum and rhodium used in catalytic converters?

    • They provide surfaces where CO and NO adsorb and their bonds weaken, allowing reaction
    • They raise the temperature of the exhaust gas so that the reaction is driven forward
    • They are the only metals that dissolve CO in the exhaust gas stream, which removes it
    • They react with CO2 and NO to form stable salts that are then removed in the exhaust

  11. In the contact process, how does the oxidation state of vanadium change as the catalyst works?

    • It changes between +5 and +4
    • It changes between +2 and +3
    • It is reduced to 0
    • It stays at +5 throughout

  12. Which description of the V2O5 mechanism in the contact process is correct?

    • O2 reduces V2O5 to V metal, which reacts with SO2
    • SO2 reduces V2O5 to V2O4
    • SO2 oxidises V2O5 to V2O6, which decomposes to O2
    • V2O5 is consumed and not regenerated

  13. Why are transition metals good catalysts?

    • They always raise the activation energy of reactions, which makes the reaction slower overall
    • Their variable oxidation states let them accept and donate electrons, forming intermediates
    • Their full d subshells block reactions, which is why they are poor catalysts in all cases
    • They are effective only in reactions of gases, where the reactant molecules collide more often

  14. Why is the uncatalysed reaction between I- and S2O8 2- slow?

    • Both ions are negatively charged and repel each other, giving a high activation energy
    • Persulfate is inert in all conditions
    • Iodide is a strong oxidant that reacts too quickly
    • The reaction is strongly endothermic with a large positive enthalpy change

  15. Which statement about a catalytic converter is correct?

    • It requires a liquid catalyst that is consumed by the reaction and must be topped up
    • It increases CO emissions to protect the engine from the heat of the exhaust gases
    • It works only at low temperatures, so it is switched off when the engine is hot
    • It reduces CO and NO emissions by converting them to CO2 and N2 on the catalyst surface

  16. Why does a catalyst not change the position of an equilibrium?

    • It lowers the activation energy of the forward and reverse reactions equally
    • It changes the enthalpy change of the reaction, so the equilibrium lies further to the right
    • It favours the forward reaction only, so more products form at equilibrium than before
    • It increases the equilibrium constant, because the catalyst makes the products more stable

  17. Why does the MnO4-/C2O4 2- reaction appear slow at first and then fast?

    • The rate is constant because MnO4- is in excess
    • Mn2+ inhibits the reaction, so the rate falls with time
    • The reaction is fast at first and stops once Mn2+ forms
    • Few Mn2+ ions are present at first

  18. Why must a heterogeneous catalyst have a large surface area?

    • Reaction occurs on the surface
    • A larger surface area shifts the equilibrium
    • Surface area has no effect because the catalyst is a solid
    • Large surface area lowers the activation energy directly

  19. What is the economic benefit of using catalysts in industrial reactions?

    • Catalysts raise the temperature needed for the reaction, which increases the energy cost of the process
    • Catalysts increase the yield of every reaction, so the equilibrium yield is always higher
    • Catalysts are consumed in the reaction, so they must be replaced at great cost each year
    • Lower activation energy allows lower temperatures and pressures, reducing energy costs

  20. A catalyst lowers the activation energy of a reaction with dH = -92 kJ mol-1. What happens to dH?

    • It becomes zero
    • It becomes more negative by the amount of the activation energy reduction
    • It becomes less negative
    • It stays -92 kJ mol-1, because dH depends only on the states of reactants and products

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