Reactions of alkanes
•The alkanes are insoluble in water but are soluble in non-polar solvents.
•There are weak dispersion forces between molecules as evidenced by their low melting and boiling points.
•Most reactions involving alkanes are either combustion or substitution.
Fuel + Oxyen --> Carbon dioxide and water
•Eg: CH4 (g) + 2O2 (g) → CO2 (g) + 2H20 (g) + energy
Chlorine atoms take the place of one or more of the hydrogen atoms.
•Eg: CH4 (g) + Cl2 (g) → CH3Cl (g) + HCl (g)
Methane combustion diagram By Jynto Robert A. Rohde Jacek FH Jynto [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Methane substitution diagram V8rik at English Wikipedia [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons
Reactions of alkenes
Ethene is the first member of the Alkenes homologous series.
Properties of Ethene (C2H4):
•Is a non-polar molecule
•Is insoluble in water
•Is a flammable gas
•Participates in addition reactions
•Polymerises to produce polyethene.
Fuel + Oxygen → Carbon Dioxide + Water
•Eg: C2H4 (g) + 3O2 (g) → 2CO2 (g) + 2H20 (g)
C=C double bond is broken and one atom is added to each carbon atom to form a molecule that has only C-C single bonds.
•Eg: C2H4 (g) + Cl2 (g) → C2H4Cl2 (g)
ethene 1,2 – dichloroethane
•Ethene also reacts with H2O to form an alcohol. H3PO4 is used as a catalyst along with a 300oC temperature to speed up the reaction.
Reaction with water is called hydrolysis.
•A polymer is made up of a repeating unit or monomer. Each monomer is added onto the end of the chain – hence the name: addition polymerisation.
•Monomers must contain a double bond. The double bond breaks to form a single bond and the free electrons form new bonds linking the monomer onto the chain.
A polymer made from more than one monomer is called a copolymer.
•Polyester is a copolymer made from di-alcohol and di-carboxylic acid monomers.
•Condensation reactions form water as a product
•The alcohol has two hydroxy groups and the carboxylic acid has two carboxy groups. These monomers combine in a condensation reaction to form polyester chains.
•Polyester has many uses in packaging and can be blow moulded to make soft-drink bottles. Some polyesters can be cross-linked, making them suitable for use as surface coatings, including paints.
.Haloalkanes (-X where X is a halogen).
•Halogen – Group VII elements eg: Cl, Br, I
•Halogen replaces hydrogen atom.
•Example: chloromethane, CH3Cl (anaesthetic)
•Chlorine is highly electronegative- making the chloroalkane molecule polar. Chlorine readily reacts with other polar molecules like water, hydroxide ions and ammonia in a substitution reaction.
Ethene addition reaction diagram Wikimedia commons.