What type of reaction occurs when multiple reactants combine to form a single product, often releasing energy?

The type of reaction where multiple reactants combine to form a single product is characterized as a synthesis reaction. In this process, two or more simpler substances come together to create a more complex compound. Synthesis reactions are often exothermic, meaning they release energy as a part of the reaction, which can manifest as heat or light.

In the context of chemistry, this type of reaction is foundational because it builds larger molecules that are essential in various biological, chemical, and industrial processes. The formation of a product from simpler components exemplifies a key principle of chemical bonding and molecular formation.

Other types of reactions listed do not fit this definition: decomposition reactions break down a compound into simpler products, exchange reactions involve the trading of components between compounds, and combustion reactions are typically a specific type of reaction that involves a fuel reacting with oxygen, leading to the release of energy, but they specifically aren't solely focused on combining reactants to form a new product.