Celebrate With Chemistry

Chemistry is the study of matter and the changes that take place with that matter.

Wednesday, August 02, 2006


the family of alkenes are said to be unsaturated hydrocarbons.

The Alkene Names, And Its General Formula.

*no methene available


alkene molecules can be prepared by cracking alkanes.
hydrogen is formed as a result of the cracking process.
alternatively, medium-sized alkanes undergo cracking
to form smaller, more useful
alkanes (octane for petrol)
and alkenes (ethene)

which can be used to form plastics like polyethene.
(for a diagram, refer to page 272 of our comprehensive chemistry text book.)


alkene + oxygen -> water + carbon dioxide

Addition Reaction

*characteristic reaction of unsaturated compounds
*addition reaction is fater than substitution reactions

alkene + hydrogen -> alkane

bromine decolourises from brown to colourless when reacted with alkenes.
hence the bromine test is used to distingush alkenes from alkanes.

alkene + water -> alcohol

alkenes can join together to form giant molecules called polymers.
*polymer = thousands of identical units called monomers joined together.

eg. the polymer - polyethene, is made up of many ethene monomer molecules.
(this will be further explained in the unit macromolecules. yuck. =P)

in short,

-the general formula for alkenes is Cn H2n.

-alkenes are often formed by cracking alkanes.

-combustion products are CO2 and water.

-alkenes undergo addtion reactions as they are unsaturated molecules because they contain double carbon-carbon covalent bonds.

-alkenes can undergo polymerisation.



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