A combination reaction, also known as a synthesis reaction, occurs when two or more reactants combine to form a single product. This type of reaction can involve elements or compounds, and it is represented by the general equation: A + B → AB. Combination reactions are common in both organic and inorganic chemistry and play a crucial role in various chemical processes. These reactions are essential in the formation of new substances, such as when hydrogen gas reacts with oxygen gas to produce water. Combination reactions are often exothermic, releasing energy in the form of heat or light, which can be observed in many everyday chemical reactions.