Catalysts
A catalyst is a substance that increases the rate of a reaction without being used up. Catalysts are vital in industry: they reduce energy demand, allow lower-temperature processes and shape the products.
How a catalyst works
A catalyst provides an alternative reaction pathway with a lower activation energy (Ea). With a lower Ea, a greater proportion of colliding particles have enough energy to react, so the rate increases.
The catalyst is regenerated at the end — it's not in the overall equation.
On a reaction profile, a catalyst lowers the "hump" but leaves the reactant and product energies unchanged. It does not alter the overall energy change ΔE.
Industrial examples
- Iron for the Haber process: N₂ + 3H₂ ⇌ 2NH₃.
- Vanadium(V) oxide V₂O₅ for the Contact process (sulfuric acid).
- Nickel for hydrogenation of alkenes (margarine production).
- Zeolites for catalytic cracking of long-chain hydrocarbons.
Biological catalysts: enzymes
Enzymes are proteins that catalyse biochemical reactions in living things. Examples:
- Amylase breaks down starch.
- Catalase breaks down H₂O₂ to water and oxygen (in liver and yeast).
Enzymes work at body temperature; they are highly specific to their substrate (lock-and-key model).
Why use catalysts industrially?
- Lower temperature needed → less energy → cheaper, lower CO₂ emissions.
- Faster production of valuable products.
- Longer-lasting — most catalysts can be reused for years.
How to spot a catalyst experimentally
A small amount that:
- Speeds up the reaction.
- Is recovered unchanged at the end.
✦Worked example— Worked example — H₂O₂ decomposition
2H₂O₂ → 2H₂O + O₂.
Without catalyst: very slow at room temperature. With manganese(IV) oxide MnO₂ (a black powder): vigorous fizzing, oxygen given off rapidly. The MnO₂ can be recovered, weighed, found unchanged.
⚠Common mistakes
- "Catalysts make reactions exothermic." No — they don't change ΔE.
- "Catalysts shift equilibrium." No — they speed up forward AND reverse equally; equilibrium position is unchanged. (See C6.5.)
- Saying catalysts "produce energy." They don't.
- Confusing catalyst with reactant. Catalysts are NOT in the overall equation.
Links
Extends C6.2 (factors affecting rate). Used in C6.4–C6.5 (equilibrium HT), C7.4 (catalytic cracking), C10.10 (Haber process HT).
AI-generated · claude-opus-4-7 · v3-deep-chemistry