Catalysts
A A substance that changes the rate of a chemical reaction without being changed by the reaction itself. is a substance that increases the rate of reaction, but can be recovered, unchanged at the end.
Only a very small The amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g). 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.
| Catalyst | Reaction catalysed |
| Iron | The Haber process (making ammonia) |
| Vanadium (V) oxide | The contact process (a stage in making sulfuric acid) |
| Manganese dioxide | Decomposition of hydrogen peroxide (produces water and oxygen) |
| Catalyst | Iron |
|---|---|
| Reaction catalysed | The Haber process (making ammonia) |
| Catalyst | Vanadium (V) oxide |
|---|---|
| Reaction catalysed | The contact process (a stage in making sulfuric acid) |
| Catalyst | Manganese dioxide |
|---|---|
| Reaction catalysed | Decomposition of hydrogen peroxide (produces water and oxygen) |
Notice that these catalysts are transition metals or A substance formed by the chemical union of two or more elements. of A metal that is located in between group 2 and group 3 (labelled as group 13 on some modern periodic tables) and has brightly coloured compounds..
How catalysts work
A catalyst provides an alternative The sequence of reactions needed to produce a desired product from a particular set of raw materials. that has a lower The minimum amount of energy that colliding particles must have for them to react. 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 Chart showing how the energy of reactants and products changes during a reaction.. This shows how the energy of the A substance that reacts together with another substance to form products during a chemical reaction. and A substance formed in a chemical reaction. change during a reaction.
Enzymes
An A protein which catalyses or speeds up a chemical reaction. 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 Scale of acidity or alkalinity. A pH (power of hydrogen) value below 7 is acidic, a pH value above 7 is alkaline..
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.
A unicellular fungus used in the brewing and baking industries. is a single-celled A large group of eukaryotic organisms that contain single celled yeasts, moulds and mushrooms.. The enzymes in yeast are used to produce wine, beer and other alcoholic drinks by Type of anaerobic respiration carried out by yeast. of sugars.