The chemical industry makes use of a wide range of chemical reactions and physical processes. In chemical reactions, elements or compounds are changed into new compounds - such as the oxidation of sulphur dioxide to sulphur trioxide. In physical processes, the physical state of something is changed, without altering its chemical identity - such as distilling a mixture of liquids into their separate components.

Chemical reactions
The thousands of chemical reactions that occur naturally, or that chemists can arrange, are grouped into types depending on the nature of the chemical change taking place. Some of the most important types of reaction used in the chemical industry are:

- Cracking
- Electrolysis
- Esterification
- Fermentation
- Halogenation
- Hydrogenation and dehydrogenation
- Hydrolysis
- Oxidation and reduction
- Polymerisation

Some reactions occur simply by mixing the starting compounds (the reactants) under the right physical conditions such as temperature and pressure. Many, however, require the use of a suitable catalyst, which plays some part in the process to increase the rate of the desired reaction, but which itself ends up unchanged. In industry, chemical reactions can be carried out as batch processes, where the reactants, often dissolved in a suitable solvent, are simply brought together in a vessel and the desired product is separated and purified from the resulting mixture. Or they can take the form of continuous processes, using equipment which allows a steady state to be reached in an operation which can be continued for days or months, with reactants being continuously fed in to the reactor, and products being pumped out and separated.

Physical processes
Physical processes are employed to prepare materials and arrange the right conditions for the chemical reaction; to control the course of the reaction itself; to separate, purify, and recycle the products, by-products and solvents used; and to ensure minimum discharge of materials into the environment. In many cases, such operations require a combination of physical and chemical, or biological, processes. Some of the physical processes most often used in the chemical industry are:

- Centrifuging
- Distillation
- Filtration
- Heating, cooling, heat-exchange
- Pressure and vacuum generation