A synthesis reaction is a chemical reaction in which two components, or reactants, come together and produce a single product. This type of a reaction can be represented as "A + B results in AB." Synthesis reactions can also be referred to as composition, construction, combination or direct combination reactions.
The reactants in a synthesis reaction can be either elements or compounds, but the result, or product of the reaction, will always be a single compound. An example of two elements combining in a synthesis reaction would be the reaction of sulfur and oxygen to produce the compound sulfur dioxide, which can be expressed as "S + O2 results in SO2." An example of two compounds combining in a synthesis reaction would be carbon dioxide and water forming carbonic acid, a new compound. This reaction can be expressed as "CO2 + H2O results in H2CO3."
Some other types of chemical reactions are cascade, decomposition and precipitation reactions. In a cascade reaction, a single reactant undergoes multiple chemical transformations. Decomposition reactions involve a compound undergoing a change that causes it to break apart into two or more components, such as sodium bicarbonate breaking down into sodium carbonate, water and carbon dioxide when heated. In precipitation reactions, a solid product, or precipitate, is formed when two aqueous reactants combine.