What Is a Catalyst and How Does It Work?

Reactions occur when particles collide with enough energy and at the correct orientation. Activation energy (Ea) is the threshold energy required for a successful collision.

A catalyst works by offering an alternative reaction pathway with a lower activation energy. Because more particles now have enough energy to react, the reaction rate increases.

Key exam point:
Catalysts do not shift the equilibrium position.
They simply help the system reach equilibrium faster.

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Energy Profile Diagrams

IB Chemistry frequently tests your ability to interpret or draw energy profile diagrams. In a catalyzed vs uncatalyzed reaction:

• The catalyzed pathway has a smaller "hump" (lower Ea).
• Reactant and product energy levels stay the same.
• ΔH remains unchanged.

Be prepared to label activation energy for both catalyzed and uncatalyzed pathways clearly.

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Types of Catalysts

Catalysts can work in different ways depending on the reaction type.

Heterogeneous Catalysts

These are in a different phase from the reactants (often solid catalysts with gaseous reactants). They work by:

• Adsorbing reactants
• Weakening bonds
• Allowing reactions to occur on the catalyst surface
• Releasing products afterward

Examples include Fe in the Haber process and V₂O₅ in the Contact process.

Homogeneous Catalysts

These are in the same phase as the reactants, often functioning through intermediate formation. They lower activation energy by offering new reaction pathways with easier steps.

Enzymes

Biological catalysts that are highly specific. They use active sites to bind substrates, drastically lowering activation energy.

Real-World Applications

Catalysts play essential roles in:

• Industrial synthesis (e.g., fertilizers, plastics, fuels)
• Environmental protection (catalytic converters)
• Biological systems (enzymes in respiration and digestion)
• Green chemistry (reducing energy consumption and waste)

In IB exams, you may be asked to connect these examples to sustainability or efficiency discussions.

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Frequently Asked Questions

Does a catalyst change the amount of product formed?

No. A catalyst speeds up the rate at which equilibrium is reached but does not change the equilibrium position or the final yield.

Why is a catalyst not consumed in the reaction?

Because it participates in intermediate steps but is regenerated before the reaction cycle ends. It facilitates reactions without being permanently altered.

Why do enzymes denature?

Enzymes are proteins, and their catalytic activity depends on their shape. High temperatures or extreme pH disrupt their structure, preventing substrate binding.

Conclusion

A catalyst speeds up a chemical reaction by lowering activation energy and providing an alternative pathway. It remains chemically unchanged and does not affect equilibrium position or enthalpy. Understanding catalysts is essential for mastering kinetics, equilibrium, and industrial chemistry in IB Chemistry.

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