Catalysts

Definition

Substances that speed up a chemical reaction without being consumed or permanently changed in the process, by lowering the energy barrier the reaction must cross.

Key points

• A catalyst lowers the activation energy, so the reaction proceeds faster, but it does not alter how much product can ultimately form (the position of equilibrium) and is recovered unchanged at the end.
• A positive catalyst speeds a reaction; an inhibitor (negative catalyst) slows it.
• Enzymes are biological catalysts (proteins) that drive reactions in living cells at body temperature.
• Industrial examples: iron in the Haber process (making ammonia for fertilisers), vanadium pentoxide in the Contact process (making sulphuric acid), and platinum, palladium, and rhodium in vehicle catalytic converters that cut harmful exhaust gases.
• Catalytic converters reduce carbon monoxide and unburnt hydrocarbons in vehicle exhaust, an environmental and air-pollution control measure.

Why it matters for CAPF

Catalysts, activation energy, enzymes, the Haber process, and catalytic converters are recurring chemistry and environment facts with an air-pollution angle.

Common confusion

A catalyst changes the rate, not the amount, of product and is not used up; do not confuse it with a reactant. Enzymes are catalysts but are highly specific and sensitive to temperature and pH, unlike most industrial catalysts.

Related concepts

concept enzymes, concept acids bases and salts, concept fuel cells and hydrogen

Parent note

chemistry everyday