Catalysts

A catalyst is a substance that increases the rate of reaction, but can be recovered, unchanged at the end.

Only a very small mass of catalyst is needed to increase the rate of a reaction. However, not all reactions have suitable catalysts.

Different substances catalyse different reactions. The table describes three common catalysts.

CatalystReaction catalysed
IronThe Haber process (making ammonia)
Vanadium (V) oxideThe contact process (a stage in making sulfuric acid)
Manganese dioxideDecomposition of hydrogen peroxide (produces water and oxygen)

Notice that these catalysts are transition metals or compounds of transition metals.

How catalysts work

A catalyst provides an alternative reaction pathway that has a lower activation energy than the uncatalysed reaction. This does not change the rate of collisions. However, it does increase the rate of successful collisions because a greater proportion of collisions now exceeds this lower activation energy.

The effect of a catalyst on the activation energy is shown on a chart called a reaction profile. This shows how the energy of the reactants and products change during a reaction.

A reaction profile for a reaction with and without a catalystA reaction profile for a reaction with and without a catalyst

Enzymes

An enzyme is a biological catalyst. Enzymes are important for controlling reactions in the cells of living organisms. They work best within a narrow range of temperature and pH.

Some enzymes can be adapted or made for use in industry. The conditions that the enzymes work in is limited but this can bring benefits. For example, the use of enzymes allows some industrial reactions to happen at lower temperatures and pressures than traditionally needed. This helps to reduce energy demands.

Enzymes are used in everyday products such as washing powders, where they break down food stains.

Yeast is a single-celled fungus. The enzymes in yeast are used to produce wine, beer and other alcoholic drinks by fermentation of sugars.