Catalysts are one of those IB Chemistry ideas that feel simple until you try to explain them under exam pressure.
You know the line: “A catalyst speeds up a reaction.”
But then a question asks for an energy profile diagram, or whether equilibrium shifts, or why the catalyst “isn’t used up,” and suddenly your confident sentence turns into a paragraph of half-true things. The good news is that catalysis is actually a calm, connected story in IB Chemistry: kinetics gives you the rate, energetics gives you the diagram, equilibrium gives you the final amounts, and applications give you the why this matters.
Quick catalyst checklist (the marks you don’t want to donate)
For most IB Chemistry structured questions, you want these points ready to go:
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A catalyst increases the rate of reaction.
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It provides an alternative reaction pathway.
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That pathway has a lower activation energy (Ea).
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The catalyst is regenerated (not consumed overall).
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ΔH does not change because reactants and products are the same.
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Equilibrium position does not change (K stays the same); equilibrium is just reached faster.
If you want a syllabus-aligned set of definitions you can quote cleanly, pair this with R2.2.5 Catalysts Notes and then test yourself using the Flashcards for R2.2.5 Catalysts.
What is a catalyst in IB Chemistry?
In IB Chemistry, a catalyst is a substance that increases the rate of a chemical reaction without being used up overall.
That last phrase matters. A catalyst can react in the middle of a mechanism (forming intermediates), but by the end it is reformed. So if an exam question asks whether it is “consumed,” your answer is essentially: it participates, but is regenerated, so it is not consumed overall.
You’ll meet catalysts in three common forms:
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Heterogeneous catalysts (different phase from reactants, often a solid surface)
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Homogeneous catalysts (same phase as reactants, often via intermediates)
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Enzymes (biological catalysts, highly specific)
For the bigger revision map of where catalysis sits in your course, start from the IB Chemistry Resources hub and branch outward by topic as you practise.
How a catalyst works: the alternative pathway (lower Ea)
A reaction doesn’t happen because particles collide. It happens because they collide with:
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enough energy to overcome activation energy (Ea)
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a workable orientation
A catalyst changes the route, not the destination. In IB Chemistry language:
A catalyst increases the rate of reaction by providing an alternative pathway with lower activation energy.
Lower Ea means a larger fraction of particles have energy ≥ Ea at the same temperature, so more successful collisions per unit time occur. That’s why rate increases.
If you’re doing HL, this links beautifully to the Arrhenius equation (and exam questions love that link). RevisionDojo breaks it down in Arrhenius Equation Explained for IB Chemistry.
Energy profile diagrams: what changes and what never changes
Energy profile diagrams are where many IB Chemistry students lose marks in silence. The rule is steady:
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The catalyzed curve has a lower peak (lower Ea).
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The reactant energy and product energy stay the same.
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Therefore ΔH stays the same.
So if you’re asked to draw both pathways, you draw two curves starting and ending at the same levels, but with different peak heights. Then you label Ea (uncatalyzed) and Ea (catalyzed) clearly.
A catalyst makes the “hill” smaller. It does not change where the hill starts or ends.
Catalysts and equilibrium: faster arrival, same final mixture
Here’s the mental model that earns marks in IB Chemistry:
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A catalyst increases the rates of the forward and reverse reactions.
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Because both directions speed up, equilibrium is reached sooner.
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But the equilibrium constant K depends on temperature (and thermodynamics), not on catalysts.
So when a question asks whether a catalyst “increases yield,” the precise answer is:
- For equilibrium reactions: No. It changes how fast equilibrium is reached, not where equilibrium lies.
Types of catalysis you should be able to describe
Heterogeneous catalysis (surface steps)
In IB Chemistry, heterogeneous catalysis is usually a story of surfaces:
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reactants adsorb onto the catalyst surface
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bonds weaken and particles align more effectively
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products form and desorb
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the surface is available again
Classic industrial examples often cited include iron in the Haber process and vanadium(V) oxide in the Contact process.
If you want a clean compare-and-contrast structure you can reuse in Paper 2, see IB Chemistry: Heterogeneous vs Homogeneous Catalysis.
Homogeneous catalysis (intermediates and mechanisms)
Homogeneous catalysis is “same phase,” but the bigger exam point is mechanism: the catalyst forms intermediates, creating multiple smaller-Ea steps instead of one big barrier.
This is where students often forget to say the catalyst is regenerated. Mention it anyway. It’s usually the final mark.
Enzymes (biological catalysts)
Enzymes are catalysts with personality: they are specific (active site fits substrate), and their activity depends on conditions like temperature and pH.
In IB Chemistry, you’re often expected to connect enzyme action back to the same fundamentals: lower Ea, alternative pathway, catalyst regenerated.
How to revise catalysts efficiently with RevisionDojo
The fastest way to make catalysis exam-ready is to run a tight loop:
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Study Notes first (clarity) using R2.2.5 Catalysts
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Flashcards next (definitions and phrasing) with Flashcards for R2.2.5 Catalysts
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Questionbank last (marks) via the Chemical Kinetics HL Questionbank
Then use AI Chat to challenge your explanation (for example: “Mark my 2-mark definition of a catalyst”). If you’re building exam stamina, pull a mixed set from Mock Exams or Predicted Papers at Chemistry Predicted Papers (Free) and practise writing catalyst explanations quickly and neatly.
Conclusion: the IB Chemistry sentence that keeps paying you back
A catalyst in IB Chemistry is your reminder that speed and outcome are different things. It increases reaction rate by providing an alternative pathway with lower activation energy, is regenerated (not consumed overall), and does not change ΔH or the equilibrium position.
If you want this to become automatic under time pressure, build the habit on RevisionDojo: learn it in Study Notes, lock the phrasing with Flashcards, prove it with the Questionbank, then polish your exam technique with Mock Exams, Grading tools, and Predicted Papers. That’s how a definition turns into marks.