Addition reactions are a type of chemical reaction where two or more substances combine to form a single product. This process typically involves unsaturated compounds, such as alkenes and alkynes, which contain double or triple bonds. When these bonds break, new atoms or groups are added to the molecule, resulting in a saturated compound. These reactions are important in organic chemistry and are commonly used in the synthesis of various chemicals, including plastics, pharmaceuticals, and fuels. Common examples include the hydrogenation of alkenes, where hydrogen is added to convert them into alkanes, and the addition of halogens to form dihalides.