CC6.2 — Catalysts (Edexcel 1SC0)

Catalysts

A catalyst increases the rate of a reaction without being used up. It provides an alternative reaction pathway with a lower activation energy.

• Catalyst is not consumed — can be reused.
• Does not change the products or the position of equilibrium (in reversible reactions).
• Lower Ea → more particles have sufficient energy → more successful collisions.

Heterogeneous vs homogeneous catalysts

• Heterogeneous: different state from reactants (e.g. iron catalyst in Haber process — solid catalyst; gaseous reactants).
• Homogeneous: same state as reactants (e.g. acid catalyst in esterification — all liquid).

Enzymes as biological catalysts

Enzymes are protein catalysts in living organisms. They work by the lock-and-key mechanism (see CB1.2). Each enzyme is specific to one substrate.

• Optimum temperature ~37°C for human enzymes.
• Denatured by high temperatures or extreme pH.
• Examples: amylase (breaks down starch), lipase (fats), protease (proteins).

Industrial catalysts

• Iron → Haber process (NH₃ production).
• Vanadium(V) oxide (V₂O₅) → Contact process (H₂SO₄ production).
• Platinum/palladium → catalytic converters in cars.