Which type of chemical reaction involves the combination of substances to form a new product?

The synthesis reaction is characterized by the combination of two or more reactants to form a single new product. This process can be represented by the general equation: A + B → AB, where A and B are the reactants, and AB is the resultant product. Synthesis reactions are fundamental in chemistry as they illustrate how different elements or compounds can interact to create new substances, which is a crucial concept in understanding chemical changes and the formation of compounds.

Decomposition reactions represent the opposite process, where a compound breaks down into simpler substances, while combustion involves a substance reacting with oxygen, typically producing heat and light. Replacement reactions involve one element being displaced by another in a compound, further differentiating them from the combination process that defines synthesis reactions.