13.3 Reactions of alkenes

why are alkenes more reactive than alkanes

1) alkenes have a pi bond 2) pi electron density is concentrated above and below the plane of the sigma bond 3) pi electrons are more exposed than the electrons in the sigma bond therefore the pi bond readily breaks

name 4 substances alkenes have addition reactions with

1) hydrogen in the presence of a nickel catalyst 2) halogens 3) hydrogen halides 4) steam in the presence of an acid catalyst

describe hydrogenation of alkenes

when an alkene is mixed with hydrogen and passed over a nickel catalyst at 423K an addition reaction takes place to form an alkane

describe halogenation of alkenes

alkenes react with the halogens chlorine or bromine at room temperature to form haloalkanes

describe a positive test for unsaturation

bromine water (orange) + alkene = haloalkane (colourless)

describe addition reactions of alkenes with hydrogen halides

alkenes react with gaseous hydrogen halides at room temperature to form multiple haloalkanes

how do addition reactions of alkenes with hydrogen halides occur when the alkene is a gas

reaction takes place when the two gases are mixed

how do addition reactions of alkenes with hydrogen halides take place when the alkene is a liquid

the hydrogen halide is bubbled through it

describe hydration reactions of alkenes

alkenes react with steam in the presence of a phosphoric acid catalyst H₃PO₄ to form alcohols

diagram of formation of a pi bond