Catalysts are one of the most important ideas in IB Chemistry, appearing in kinetics, equilibrium, industrial chemistry, and HL transition metal chemistry. Students often know that catalysts “speed up reactions,” but IB exams require a more precise explanation. This guide breaks down exactly what a catalyst does, how it works, and how to describe it in clear IB-friendly language.
Quick Start Checklist
A catalyst:
- Increases reaction rate
- Lowers activation energy
- Provides an alternative pathway for the reaction
- Is not consumed in the reaction
- Does not change the equilibrium position
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What Does a Catalyst Actually Do?
The key function of a catalyst is to lower the activation energy (Ea) of a reaction.
It does this by providing a new reaction mechanism or pathway that requires less energy for reactants to form products.
This increases the number of successful collisions per unit time, which increases reaction rate.
In IB terms:
“A catalyst increases the rate of reaction by providing an alternative pathway with lower activation energy.”
This exact phrasing earns marks consistently.
How a Catalyst Affects Collisions
1. More particles have sufficient energy
With a lower Ea, a greater fraction of molecules have energy ≥ activation energy.This dramatically increases the rate of successful collisions.
