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Ethene, Polymers and Ethanol
Ethene is a product of the catalytic cracking of crude petroleum and is important as the
starting compound for many synthetic polymers. Ethene could also be used to produce
ethanol, a possible replacement fuel for petroleum.
Catalytic cracking
Process in which high molecular weight fractions from crude
oil are broken down into lower molecular weight substances.
This process increases the output of high demand products.
Reactions of alkanes
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Reactions of alkenes
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Burn in air to form carbon dioxide, water and large
amounts of energy.
Alkanes react with chlorine, bromine and iodine when the
mixtures are exposed to ultraviolet light. These are
substitution reactions.
Burn in air to form carbon dioxide, water and large
amounts of energy.
Undergo addition reactions with
o Hydrogen to form alkanes
o Halogens to form dihaloalkanes
o Hydrogen halides to form haloalkanes
o Water to form alkanols
Alkyl group
An alkane molecule with one hydrogen atom missing: it does
not exist by itself but is part of another molecule.
Alkanols
The alkanols are a sub-group of the class of compounds called
alcohols. They contain the –OH functional group.
Naming an alkanol
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Polymerisation
Chemical reaction in which many identical small molecules
(monomers) combine together to form one large molecule
(polymer).
Delete the “e” of the parent alkane and add “ol”.
Add a number prefix to denote the position of the alcohol
group
Addition polymers
Form by molecules joining together without the loss of any
atoms. The monomer molecules contain a double bond that
opens up to form the covalent link between molecules.
Examples of addition polymers include
 Low density polyethylene
 High density polyethylene
 Polypropylene
 Poly(vinyl chloride)
 Poly(acrylonitrile)
 Polystyrene
 Poly(tetrafluoroethylene) PTFE or Teflon
Condensation
polymers
Polymers that form by the elimination of a small molecule
(water) when pairs of monomer molecules join together.
Examples of condensation polymers include
 Cellulose
 Proteins
 Nylon 6
Formation of
polyethylene
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Low-density polyethylene contains significant chain
branching and is formed in a gas phase process involving
high pressure and high temperatures.
High-density polyethylene contains unbranched
molecules formed at relatively low pressures and low
temperatures
Properties of
polymers that relate
to their use
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Melting or softening point
Stability to heat or light
Chemical stability
Mechanical strength
Flexibility or rigidity
Structural features of
addition polymers
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Average molecular weight (chain length)
Crystallinity (extent of chain branching)
Chain stiffening
Crosslinking
Biopolymers
Polymers made totally or in large part by living organisms
Synthetic
biopolymers
Partially synthetic polymers based on cellulose and including
 Rayon
 Viscose rayon (or viscose) (cellophane)
 Cellulose nitrate (photographic or movie film, gun cotton,
celluloid)
 Cellulose acetate
Dehydration of
ethanol
Ethene the starting material for many polymers may be
produced from ethanol by a dehydration reaction using
concentrated sulfuric acid and a suitable catalyst.
H2SO4
CH3-CH2-OH
Ethanol as a solvent
CH2=CH2
+ H2O
Ethanol is a very polar molecule and readily forms hydrogen
bonds. It is a good solvent for polar substances.
Ethanol is used as solvent in
 Cosmetics
 Food colourings
 Medicinal preparations
 Cleaning agents
 Industry
Fermentation
Process in which glucose is broken down to ethanol and
carbon dioxide by the action of enzymes present in yeast.
yeast
C6H12O6(aq)
Ethanol as a fuel
2CH3-CH2-OH(aq) + 2CO2(g)
Ethanol burns readily
C2H5OH(l) + 3O2(g)
2CO2(g)
+ 3H2O(g)
Advantages
 Ethanol is a renewable resource
 Could reduce greenhouse gas emissions
Disadvantages
 Would need large areas of agricultural land
 Disposal of large amounts of smelly waste fermentation
liquors
Molar heat of
combustion
The heat liberated when one mole of the substance undergoes
complete combustion with oxygen at a constant pressure of
exactly one atmosphere.