What type of reaction involves the transfer of electrons between two species?

A reaction that involves the transfer of electrons between two species is classified as a redox reaction, short for reduction-oxidation reaction. In this type of reaction, one species undergoes oxidation, meaning it loses electrons, while another species undergoes reduction, meaning it gains those electrons. This electron transfer is fundamental to redox processes and is often accompanied by changes in oxidation states of the reacting species.

For example, in the reaction of hydrogen with oxygen to form water, hydrogen undergoes oxidation as it loses electrons, and oxygen is reduced as it gains electrons. This interconnected transfer of electrons highlights the essence of redox chemistry, which is critical in various chemical processes, including metabolic pathways, electrochemistry, and corrosion reactions.

In contrast, synthesis and decomposition reactions typically involve the formation or breakdown of compounds without a specific focus on electron transfer, while combustion reactions are a type of redox reaction but specifically involve a fuel reacting with an oxidant, usually oxygen, to produce energy, carbon dioxide, and water. Thus, while combustion reactions do involve electron transfer, the term "redox reaction" more broadly encompasses all reactions where electron transfer occurs.