Final answer:
The reactivity of alkenes in addition reactions is due to the weak pi bond in the double bond, which is more reactive than single bonds. The addition of atoms like hydrogen and halogens or water changes the double bond into a more stable single bond, leading to the formation of alkanes, halogenated compounds, or alcohols.
Step-by-step explanation:
The trend for alkene reactivity in addition reactions is influenced by the presence of a double bond between carbon atoms which is more reactive compared to single bonds found in alkanes. This reactivity is due to the pi bond (π bond) in the double bond being weaker and more susceptible to breakage during chemical reactions. For instance, in hydrogenation, hydrogen is added to an alkene in the presence of a catalyst like nickel or platinum, resulting in the alkane. The hybridization of carbon changes from sp² to sp³ as the reaction changes the double bond into a single bond with added atoms or groups. Additionally, when an alkene reacts with halogens, it also undergoes an addition reaction where the double bond is attacked and converts into a single bond with the halogen atoms attached. Similarly, the hydration reaction of alkenes with water forms an alcohol, necessitating a strong acid catalyst like sulfuric acid (H2SO4). Electrophilic addition is another pivotal reaction type in this category.