Industrial importance of alkenes

An essay type documents about the industrial importance of Alkenes for OCR Chemistry B. The important bits are highlighted and it really helps with application Questions. I'm doing A2 Chemistry now and got an A at AS so stuff like this really does work! :)

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  • Created on: 10-11-12 15:14
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Olivia Frary Chemistry
Industrial importance of Alkenes
Alkenes are a homologous series with the aliphatic general formula CnH2n; they also have a
double bond within their structure which makes them unsaturated and more reactive then a
saturated compound. It is because of this that they are useful in many industrial processes such as
Polymerisation and the Hydrogenation of unsaturated vegetable oil to make Margarine. These are
both important, useful processes which require certain conditions and reactants to make the finished
Hydrogenation is an addition reaction and the process of adding Hydrogen across a double bond, in
the presence of a Heterogeneous catalyst such as Ni, to an unsaturated vegetable oil. It is also done
under High temperatures (150°c). A simpler way to look at this would be to look at the
hydrogenation of Ethene to create a saturated Hydrocarbon- Ethane.
A simplified version of the mechanism of the reaction would also be to look at the reaction between
Ethene and Hydrogen. As the Hydrogen molecule approaches the double bond, because of the high
electron density, the bonded electrons are repelled more to one of the bonded atoms creating
partial charges (+ and -).
The Partially positive Hydrogen is then attracted to the high electron density double bond, and by
the process of Heterolytic fission, the bond between the Hydrogen breaks and the positive
Hydrogen ion bonds with one of the electrons from the Pi-Bond leaving a positive Carbocation and
negative Hydrogen Ion.

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Olivia Frary Chemistry
The Hydrogen then bonds with the Carbocation leaving a saturated molecule- Ethane.
This changes some of the Physical properties of the vegetable oil, such as the Melting point, making
it partially solidify. This is because the number of C-C double bonds can help determine the melting
point of the substance- the more C-C double bonds, the lower the melting point. If you control the
number of double bonds you saturate, you can control the texture and overall `spread ability' of the
margarine.…read more

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Olivia Frary Chemistry
For example, the Alkene in the diagram above is called Prop-1-ene, but when put under certain
conditions around other Monomer units of the same species, the Pi-bond will break down causing it
to bond with the surrounding monomer units creating PolyProp-1ene or just Polypropene.
Polypropene has many uses such as food packaging, textiles and dishwasher safe containers to name
a few.…read more

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Olivia Frary Chemistry
However, because of the very unreactive nature or saturated Polymers, they cause a lot of
environmental problems and a high amount of wastage. Polymers are non-biodegradable so they
won't break down for thousands of years, this creates unsightly land fill sites which will very soon be
too full to take anymore waste, if not dealt with properly.
One way to deal with them without harming the planet and environment is to recycle them.…read more

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Olivia Frary Chemistry
Biodegradable plastics break down as a result of bacteria and compostable plastics must break down
by biological processes to create CO2, H2O and other inorganic compounds.…read more


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