Catalyst

Summary: A substance that increases the rate of a chemical reaction without being chemically changed or used up. Provides an alternative pathway with lower activation energy. Tags: igcse chemistry definition reactions Created: 2026-07-14 Last Updated: 2026-07-14

A catalyst is a substance that increases the rate of a chemical reaction without being chemically consumed or permanently altered by the reaction, meaning it can be recovered unchanged at the end and reused. Catalysts achieve this rate enhancement by providing an alternative reaction pathway that has a lower activation energy (Ea) than the uncatalysed route, so a much greater proportion of particle collisions meet the minimum energy requirement for a successful reaction. Industrially, catalysts are of enormous economic importance because they allow reactions to proceed at lower temperatures and pressures, reducing energy costs and making processes commercially viable — key IGCSE examples include iron powder in the Haber process (N₂ + 3H₂ ⇌ 2NH₃ at 450°C), vanadium(V) oxide (V₂O₅) in the Contact process (2SO₂ + O₂ ⇌ 2SO₃), and manganese dioxide (MnO₂) in the decomposition of hydrogen peroxide. Biological catalysts are known as enzymes and are remarkable for their specificity, each enzyme typically catalysing only one specific biochemical reaction under mild conditions of temperature and pH. An absolutely critical point for IGCSE exams is that a catalyst does NOT affect the position of equilibrium in a reversible reaction nor does it change the enthalpy change (ΔH) of the reaction — it only increases the rate at which equilibrium is reached, by lowering Ea equally for both the forward and reverse reactions.

Key term — IGCSE Chemistry (0620/0971) glossary.