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K324 / 2027
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Lesson 4 of 5

Catalysts provide an easier reaction pathway

They change the rate without being used up overall.

O-Level 6092 (2026) / SEC G3 K324 (2027)

Pure only
  • I can define catalysts and their effects.Syllabus

    Syllabus K324, 10(b). Define catalysts and their effects

  • I can explain lower activation energy.Syllabus

    Syllabus K324, 10(c). Explain lower activation energy

  • I can recognise catalyst applications.Syllabus

    Syllabus K324, 10(d). Recognise catalyst applications

Catalysts provide an easier reaction pathway

They change the rate without being used up overall.

Make a guess. You are not marked.

A catalyst is added to a reaction that would otherwise be slow. What happens to the total amount of product made by the end?

  1. More product forms in total by the end
  2. It stays the same; it just forms sooner
  3. Less product forms, as the catalyst is used up
Show the answer

It stays the same; it just forms sooner

A catalyst makes the product form faster, but the amounts of reactants decide how much product can form.

A catalyst increases reaction rate and is chemically unchanged overall at the end. It can take part in intermediate steps before being regenerated. It provides an alternative pathway with lower activation energy, so a larger fraction of collisions can succeed at the same temperature. It does not supply the reaction energy or increase the final yield from a fixed limiting reactant.

Catalyst examples
ContextCatalyst or catalytic material
Haber ammonia synthesisIron
Hydrogenation of unsaturated oilsNickel
Hydrogen peroxide decompositionManganese(IV) oxide
Sulfuric-acid manufactureVanadium(V) oxide, an example of a compound acting as an industrial catalyst
Catalytic convertersMetal catalysts speed conversion of exhaust pollutants
Biological reactionsEnzymes are biological catalysts

On an energy profile, the catalysed route has a lower peak but the same reactant and product levels. Enzymes also increase rates, but their activity depends on conditions; heating them too much can change their structure and reduce activity. Do not treat every catalyst as able to work under any conditions.

Check your understanding

Adding a catalyst gives more gas after 20 s. Will it give more gas once the reaction is complete?

  1. Yes. A faster reaction converts more reactant into gas.
  2. No. It makes the same final amount of gas, just sooner.
  3. No. It makes less gas overall, because some reactant sticks to the catalyst.
Show the answer

No. It makes the same final amount of gas, just sooner.

A catalyst speeds up the reaction but does not change how much reactant there is. The final amount is set by the limiting reactant.

Exam-style question

Manganese(IV) oxide speeds up the decomposition of hydrogen peroxide, 2H2O2(aq) → 2H2O(l) + O2(g).
(a) Define the term catalyst. [1]
(b) Explain, in terms of activation energy and collisions, how manganese(IV) oxide increases the rate. [2] [3]

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Check your understanding

Which statement about enzymes is correct?

  1. They increase the final amount of product that the reaction makes
  2. They are biological catalysts that are denatured if heated too much
  3. They are used up gradually as the reaction they catalyse goes on
  4. They work faster and faster the higher the temperature is raised
Show the answer

They are biological catalysts that are denatured if heated too much

Enzymes are proteins made by living things that speed up reactions, such as yeast enzymes in fermentation. High temperatures change their shape, so they stop working.