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9.2 Production of materials: 1. Fossil fuel products
Extract from Chemistry Stage 6 Syllabus (Amended October
2002). © Board of Studies, NSW.
[Edit: 7Jul09]
Prior learning: Preliminary modules 8.2.5, 8.5.1, 8.5.2, 8.5.3, 8.5.5
Background: Fossil fuels are formed from
the remains of organisms that lived on Earth millions of
years ago. Fossil fuels are rich in hydrocarbons that can be
burnt to release energy or used to make raw materials such as
ethylene.
Ethylene is the same substance as ethene. Ethene is
the IUPAC name for C2H4 while
ethylene is the name that is more commonly used in
industry.
Ethylene (C2H4) can be used to produce
useful substances such as polyethylene and ethanol.
Polyethylene is the cheapest plastic. The weight of polyethylene produced each year is greater than the total weight of all other plastics. Most plastic food bags, juice and milk containers are made of, or lined with, polyethylene.
construct word and balanced formulae equations of chemical reactions as they are encountered
-
An important part of the Preliminary course, that you
must continue with throughout the HSC course, is learning
how to:
- construct word equations, e.g: methane +
oxygen -----> carbon dioxide +
water
and
- balance formulae equations, e.g:
CH4 + 2O2 ----->
CO2 + 2H2O
You must be able to do this for the reactions you encounter in every module that you study, core and option.
- construct word equations, e.g: methane +
oxygen -----> carbon dioxide +
water
There are three important steps involved:
- Show all reactants and all products in the word equation.
- Write the correct formula for each reactant and each product.
- Balance the formula equation by placing coefficients (numbers) in front of formulas so that you have the same total number of each kind of atom on both the reactant side and the product side. Remember that in chemical reactions atoms are just rearranged, not created or destroyed.
gather and present information from first-hand or secondary sources to write equations to represent all chemical reactions encountered in the HSC course
- It is recommended that you write equations to represent
the chemical reactions as you gather
information about them throughout this section of the
module. The information needed to write the equations might
be gathered from first-hand
investigations. You should check these against
equations published in secondary sources.
For other reactions studied, write equations as a summary
of the chemistry involved.
- When presenting equations in carbon
chemistry, the emphasis is on showing the structures of
reactants and products, not on making sure that they are
balanced. The emphasis for this section of the
syllabus is in showing structure rather than in balancing
equations.
- The following are the equations that represent the processes presented in this section of the syllabus:
identify
the industrial source of ethylene from the cracking of some
of the fractions from the refining of petroleum
- Petroleum is a mixture of hydrocarbons. When petroleum undergoes fractional distillation, some fractions, particularly petrol, are in demand and of high economic value. Other fractions, consisting of larger molecules than in petrol and of low value, can be passed over a heated catalyst that cracks the larger molecules into smaller molecules. A major by-product of this catalytic cracking is ethylene, also known as ethene.
Another way ethylene is produced . .
.
A process called steam thermal cracking is the
main source of ethylene throughout the world. In this
process ethane (C2H6) gas from
natural gas, or larger hydrocarbons in low value petroleum
fractions, are mixed with steam and passed through hot
metal coils. The steam removes carbon deposits from the
metal coils. The heat from the coils breaks bonds to change
the ethane, or the larger hydrocarbons, to ethylene.
Structure of ethylene 
Key Centre for
Polymer Colloids, University of Sydney, Australia
identify
data, plan and perform a
first-hand investigation to compare the reactivities of
appropriate alkenes with the corresponding alkanes in bromine
water
- This investigation requires comparison to indicate the
reactivities of two substances. This is most easily
achieved by direct observation of colour changes when
yellow bromine water is added to the two substances. The
type of data is qualitative. The loss of
bromine colour from the bromine water will identify that
reaction has occurred.
- This qualitative data will be valid if your
plan includes the control of variables.
Consider what must be kept the same in the investigation.
For example, make sure that the same amount of bromine
water is added and is shaken in the same way. Use
corresponding alkenes and alkanes that have similar
structures preferably differing only by the presence and
absence of a carbon to carbon double bond. Cyclohexene and
cyclohexane are suitable to use.
- When performing the investigation, ensure that correct safety procedures are used and that quantities of chemicals are kept to the minimum level to observe an effect.
identify
that ethylene, because of the high reactivity of its double
bond, is readily transformed into many useful
products
- Ethylene can be transformed into many useful products because of the high reactivity of its double bond.
An explanation
Alkenes are more chemically reactive than their
corresponding alkanes. The yellow colour of bromine water,
which is due to the presence of bromine, is lost when the
bromine water comes in contact with an alkene, but not when
in contact with an alkane. This demonstrates the high
reactivity of a
C=C in an alkene compared with the C-C in an alkane.
-
Some of the useful products made from ethylene are:
Product Formula Use polyethylene (CH2)n plastic ethylene oxide (CH2)2O steriliser ethanol C2H5OH disinfectant ethanoic acid CH3COOH food preservative
Reactivity of ethylene and Reactions of ethylene
Key Centre for Polymer Colloids, University of Sydney,
Australia
analyse
information from secondary sources such as computer
simulations, molecular model kits or multimedia resources to
model the polymerisation process
-
You can simulate and then analyse the
polymerisation process by using a molecular model kit to
construct a model of a long chain polymer from a number
of monomers, such as ethylene.
Begin with at least five separate models of the monomer. Initiate the production of the polymer by changing the C=C double bonds of two monomer models to C-C single bonds. Join the two reactive molecules with one of the single bonds (electron pairs) released when a double bond changed to a single bond. Continue this process to join the remaining monomers.
You will end up with a long chain like the following.
Remember that this simulation is a micro-view of a process that is repeated over and over in the macro-production of a polymer. The many long chains produced are held together by intermolecular forces or tangling of chains.
identify
polyethylene as an addition polymer and explain
the meaning of this term
- Polyethylene is called an addition polymer.
- An addition polymer forms when small molecules (the monomer), such as ethylene, add together to form long molecules (the polymer), such as polyethylene, and no other product.
Addition polymerisation Key Centre for
Polymer Colloids, University of Sydney, Australia
identify
that ethylene serves as a monomer from which polymers are
made
-
Ethylene is polymerised to polyethylene
- High pressures produce soft, low density polyethylene
(LDPE) consisting of tangled chains (with molecular masses
< 100 000); used in flexible plastic bags such as those
used to store food.
- Low pressures produce harder, high density polyethylene (HDPE) consisting of aligned chains (with molecular masses > 100 000); used in crinkly plastic bags as used for heavy duty garbage bags.
Polyethylene Key Centre for Polymer
Colloids, University of Sydney, Australia
outline
the steps in the production of polyethylene as an example of
a commercially and industrially important polymer
- Two different forms of polyethylene can be
manufactured, depending on the reaction conditions.
- To produce low density polyethylene (LDPE), a peroxide
containing an O-O bond that breaks easily forming free
radicals is used to initiate the joining of ethylene
monomers. The process must occur under high gas pressure to
produce LDPE. These production conditions result in
molecules with the short branches that characterise LDPE.
- To produce high density polyethylene (HDPE), low gas pressures and a catalysts made of transition metals and organometallic compounds enables more ordered orientation of ethylene to form the long unbranched and aligned molecules in HDPE.
Free Radical Polymerisation and Polyethylene production ,
Key Centre for Polymer Colloids, University of Sydney,
Australia
identify the following as commercially significant monomers:
- vinyl chloride
- styrene
by both their systematic and common names
describe the uses of the polymers made from the above monomers in terms of their properties
The following information addresses the above two syllabus
points at the same time.
-
The table below provides the systematic and common names
for some commercially significant monomers. The table
describes the properties that account for the uses of
some polymers produced from the selected monomers.
MONOMERS POLYMERS Common name Systematic name Name Properties Used for ethylene ethene LD polyethylene low density, soft flexible food bags HD polyethylene high density, hard crinkly garbage bags vinyl chloride chloroethene polyvinylchloride made rigid and flame resistant with additives, water resistant rigid pipes and gutters,
flexible raincoats and shower curtainsstyrene ethenylbenzene polystyrene transparent, due to few crystals,
when gas added forms foamcompact disc cases,
heat insulation, floats
- Expanded polystyrene is made by producing gas bubbles inside polystyrene. The low density of expanded polystyrene is used in flotation devices. The trapped gas spaces make it an excellent insulator.
This site is useful for links to information about polystyrene, PVC (polyvinylchloride) and polyacrylonitrile.
Properties of polymers Key Centre for
Polymer Colloids, University of Sydney, Australia
Polyethylene (polyethene) From
Wikipedia, the free encyclopedia
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