Catalysts and Reversible Reactions

This lesson brings together two important topics from the AQA GCSE Combined Science Trilogy (8464) specification: catalysts and reversible reactions. You need to understand how catalysts work, their importance in industry, and how reversible reactions differ from irreversible reactions.

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Catalysts

What Is a Catalyst?

A catalyst is a substance that increases the rate of a chemical reaction without being used up in the process. It can be recovered chemically unchanged at the end of the reaction.

How Do Catalysts Work?

Catalysts provide an alternative reaction pathway with a lower activation energy.

$\text{Activation energy (with catalyst)} < \text{Activation energy (without catalyst)}$Activation energy (with catalyst)<Activation energy (without catalyst)

Because the activation energy is lower, a greater proportion of colliding particles have enough energy for a successful collision. This means more reactions happen per second — the rate increases.

Key Point: A catalyst does NOT change the overall energy change (ΔH) of a reaction. The energy of the reactants and products remains the same. Only the activation energy is lowered.

Energy Profile Diagram