If a chemical reaction forms a single product from more than one reactant, it is called a synthesis reaction or a combination reaction.

Here's a breakdown:

* Synthesis Reaction: This term emphasizes the creation of a new, more complex molecule from simpler ones.

* Combination Reaction: This term focuses on the joining of two or more substances to form a single product.

General Form:

A + B → AB

Example:

* Formation of water: 2H₂ (hydrogen) + O₂ (oxygen) → 2H₂O (water)

In this example, two reactants (hydrogen and oxygen) combine to form a single product (water).