What type of reaction involves the combination of two smaller molecules to form a larger molecule?

A synthesis reaction, also known as a combination reaction, is characterized by the merging of two or more reactants to produce a single, more complex product. This type of reaction is fundamental in the field of chemistry as it forms the basis for creating larger and more complex molecules from simpler building blocks.

In practical terms, synthesis reactions are observable in various chemical processes, such as the formation of water from hydrogen and oxygen gases. The formula for such a reaction can be represented as 2H₂ + O₂ → 2H₂O. This highlights how smaller molecules (hydrogen and oxygen) combine to create a larger molecule (water).

Other types of reactions, such as decomposition, single replacement, and combustion, do not involve the direct combination of smaller molecules into a larger one but rather involve breaking down compounds, exchanging components, or reacting compounds with oxygen in the case of combustion.