A synthesis reaction, also known as a direct combination or combination reaction, is a chemical process in which two or more simple elements or compounds combine to form a more complex product. It is represented by the equation: A + B → AB.
Synthesis reactions play a crucial role in creating compounds from their constituent elements and generating larger molecules from smaller ones. They are the opposite of decomposition reactions, which break down complex substances into simpler components. Synthesis reactions are one of the major classes of chemical reactions, which include single displacement, double displacement, and combustion reactions.