A catalyst increases the rate of reaction by providing an alternative reaction pathway lowering the activation energy. They are economically important and allow chemicals to be formed cheaper, faster and safer.

A Maxwell-Boltzmann distribution showing the effect of a catalyst


Types of catalysts


Catalysts in the same phase (same physical state) as the reactants and products.


Hot concentrated sulphuric acid catalyst

Break down of ozone
Cl• catalyst The breakdown of ozone can lead to increased risks of skin cancers due to a lack of protection from UV light

Cl• formation from chloro-fluoro carbons (CFCs)

Reaction stages




Catalysts in a different phase as the reactants and products (different physical state, usually a solid).

These react of a series of steps:
1. Adsobtions (not absorption) of gaseous molecules to the catalyst surface
2. Reaction – bonds weakened on the catalyst surface lowering the activation energy
3. Desorption of product molecule from surface


· Haber process with an iron catalyst – used to make ammonia for fertilisers

N2 + 3H2 2NH3

· Isomerisation of petrol with a platinum catalyst

· Hydrogenation of vegetable oils to manufacture margarine with a nickel catalyst

CH2=CH2 + H2 CH3CH3

Car exhausts

Catalytic converters include platinum and rhodium catalysts. They are used to remove toxic carbon monoxide which is formed from the incomplete combustion of petrol, oxides of nitrogen which can lead to acid rain formed from nitrogen and oxygen reacting from the air and unburnt hydrocarbons which can lead to photochemical smog and low-level ozone.


2NO + 2CO 2CO2 + N2