Reactivity: Alkenes more reactive than alkanes as the π- electrons are more exposed than σ- bond
electrons. The π- bond is weaker than σ- bond.
• Addition Reactions: Each of these reactions involves addition of molecule across double bond,
causing π- bond (double bond) to break and form a saturated product (single bonds).
• All below are addition reactions so no gaps.
• 1) Hydrogenations of Alkenes: Alkene + hydrogen with presence of nickel catalyst at
423 K. Excess hydrogen- if two double bonds would be 2H2. Forms alkane.
• 2) Halogenation of Alkenes: Alkene + bromine/ chlorine at room temperature. Forms
haloalkane. This is the electrophilic addition below.
• Testing for Unsaturation: When aqueous bromine added to alkene, bromine added across double
bond. Goes from orange to colourless to indicate presence of C=C bond so unsaturated. Saturated
compound have no colour change.
• 3) Alkenes and Hydrogen Halide: At room temperature to form haloalkanes. Alkenes
can also react with gas which is bubbled through or hydrochloric or hydrobromic acid- solutions
of hydrogen halides. Two products formed in this reaction…
• Two Products: Two products formed when unsymmetrical reacts with another unsymmetrical
molecule. H and Cl from HCl swap places. Same method to doing isomers.
• 4) Hydration Reactions of Alkenes: Alkene + steam with phosphoric acid catalyst
(H3PO4). Forms alcohol. Like reaction above, two products possible. Have H2O with (g).
