Fuels
C1 Topic 5
What are
are fossil
fossil fuels?
fuels?
What
• Fossil fuels are formed over millions of years,
from the remains of dead organisms
- Crude oil and gas are formed from dead creatures
- Coal is formed from dead plants
• They are finite resources (limited supply)
• They are non-renewable fuels as they take so
long to form and are used up faster than they are
produced
Crude oil
oil
Crude
• Fossil fuel (finite resource)
• Complex mixture of hydrocarbons
(compounds made of hydrogen and carbon)
• Different hydrocarbons contain different
numbers of carbon and hydrogen atoms
Marine organisms die and are deprived of
oxygen. They are subjected to heat and
pressure over millions of years. This
produces crude oil
The bonds between
the atoms within a
hydrocarbon are
strong covalent bonds
The forces between the different
hydrocarbon molecules are weak
intermolecular forces
Fractional distillation
distillation
Fractional
• Separates crude oil into simpler, more useful
products called fractions (a group of
hydrocarbons with a similar carbon chain length
and boiling point)
• Fractional distillation works because the different
substances in the mixture have different boiling
points (this is the physical property than enables
crude oil to be separated)
• Substances with high boiling points condense at
the bottom, and substances with low boiling
points condense at the top
Fractions
Fractions
Each fraction contains hydrocarbon molecules with a
similar number of carbon atoms
• Gases – used in domestic heating and cooking (least carbon
atoms)
• Petrol – used as fuel for cars
• Kerosene – used as fuel for aircraft
• Diesel oil – used as fuel for some cars and trains
• Fuel oil – used as fuel for large ships and in some power
stations
• Bitumen – used to surface roads and roofs (most carbon
atoms)
NB: During
boiling,
intermolecular
forces break,
but covalent
bonds within
the molecule
do not as they
are much
stronger due
to shared
electrons
Shorter hydrocarbons,
weaker intermolecular
forces, lower boiling
points
Longer hydrocarbons,
stronger
intermolecular forces,
higher boiling points
How do fractions differ?
• The number of carbon and hydrogen atoms
their molecules contain
• Boiling points
• Ease of ignition
• Viscosity
Supply and demand
Hydrocarbons
Hydrocarbons
• The two elements chemically combined in a
hydrocarbon compound are:
- Carbon (C) – contains carbon atoms
- Hydrogen (H) – contains hydrogen atoms
• There are two main types of hydrocarbon found
in crude oil:
- Alkanes
- Alkenes
Alkanes
Alkanes
•
•
•
•
End in -ane
Contain only single covalent bonds
Saturated hydrocarbons
General formula: CnH2n+2
Alkanes
Alkanes
s
Alkane
Formula
Methane
CH4
Ethane
C2H6
Propane
C3H8
Chemical structure
Ball-and-stick
model
Alkenes
Alkenes
• End in -ene
• Contains a double covalent bond (2 shared
pairs of electrons)
• Unsaturated hydrocarbons
• General formula: CnH2n
• Can act as monomers to form polymers (under
high pressure in the presence of a catalyst)
Alkenes
Alkenes
Alkene
Formula
Ethene
C2H4
Propene
C3H6
Chemical structure
Ball-and-stick
model
Alkane or
or alkene?
alkene?
Alkane
• Bromine water test:
- Alkane: bromine water is orange/brown
- Alkene: bromine water is decolourised
Cracking
• Breaks down larger saturated hydrocarbon
molecules (alkanes) into smaller, more useful
ones, some of which are unsaturated (alkenes)
• Requires a high temperature and a catalyst
Why is cracking useful?
• Helps an oil refinery match its supply of useful
products with the demand
• Smaller alkenes that are produced can be used
to make polymers
Cracking apparatus
apparatus
Cracking
alkane e.g. liquid paraffin
alkene e.g. ethene
(gas) – will
decolourise
bromine water
Catalyst- aluminium oxide
Cracking equations
C10H22
C8H18
C2H4
What are polymers?
Polymers are very large molecules made when hundreds of
monomers join together to form long chains
The word ‘polymer’ comes from the Greek words
poly (meaning ‘many’) and meros (meaning parts)
Plastics are synthetic polymers that can be
shaped by heat or pressure
What keeps the chain together?
• The monomers in a polymer are joined
together by covalent bonds between atoms
covalent
bond
What are polymers made from?
• Many polymers are formed from alknenes, hydrocarbon
compounds with the general formula CnH2n
• Alkenes contain at least one double covalent bond between
carbon atoms. The double bond makes them very reactive
• The simplest alkene is
ethene (C2H4)
• The second simplest
alkene is propene (C3H6)
double
covalent
bond
Addition polymerisation
• Many ethene molecules can combine together in a
polymerisation reaction
• The polymer formed id called poly(ethene)
polymer

monomers
addition polymerization
Drawing polymers
• Part of the polymer molecule can be drawn:
• An easier way is to show a shorthand formula:
The ‘n’ means that the
polymer contains a very large
number of the repeating unit
shown in the brackets
Polymerisation equations
What is the polymer?
The monomer
is propene
(C3H6)
Which can
also be
drawn as:
The polymer is
polypropene
What is the monomer?
The polymer is
polychloroethene (or
polyvinylchloride- PVC)
The monomer is
chloroethene
Naming polymers
Monomer
Ethene
Propene
Chloroethene
Tetrafluoroethene
Polymer
Poly(ethene)
Poly(propene)
Poly(chloroethene) or
Polyvinylchloride (PVC)
Poly(tetrafluoroethene)
(PTFE)
Uses of polymers
Monomer
Polymer
Properties
Uses
Ethene
Poly(ethene)
Flexible, cheap,
good insulator
Plastic bags and
bottles, insulation
coating on
electrical wires
Propene
Poly(propene)
Flexible and strong Buckets and crates
Uses of polymers
Monomer
Polymer
Properties
Uses
Chloroethene
Poly(chloroethene)
or Polyvinylchloride
(PVC)
Tough, cheap
and long
lasting, good
insulator
Window
frames, gutters,
pipes,
insulation for
electrical wires
Tetrafluoroethene
Poly(tetrafluoroethene) Tough,
Non-stick
or PTFE
resistant to
coating on pans
corrosion and
non-stick
Disposing of
of polymers
polymers
Disposing
• One of the useful properties of polymers is that they
are unreactive, so they are suitable for storing food
and chemicals safely.
• This property makes it difficult to dispose of
polymers. Many polymers are non-biodegradable
(microorganisms cannot digest them, they take a
long time to break down)
• They are usually disposed of by burying them in
landfill sites or burning them in incinerators. These
methods of disposal cause environmental problems
and waste valuable resources
Landfill for polymers
• Uses up valuable land
• Sites fill up quickly
• Visual pollution
Incineration
•  Release a lot of heat energy when burnedcan be used to heat homes or generate
electricity
•  Toxic products
•  CO2 is produced, which adds to global
warming
Recycling polymers
•  Reduces disposal problems
•  Reduces amount of crude oil used
•  Different polymers must be separateddifficult and expensive
Biodegradable polymers
• Most polymers e.g. poly(ethene) and
poly(propene) are non-biodegradable,
however, it is possible to include chemicals
that cause the polymer to break down more
quickly
Combustion
Combustion
• Combustion is a rapid reaction between a substance
and oxygen that releases heat and light energy
• A fuel is a
substance that
reacts with
oxygen to
release useful
energy
Complete combustion
combustion
Complete
• Requires a plentiful supply of oxygen (air) so that the
elements in the fuel react fully with oxygen
- 21% of the air is oxygen
• Releases more energy than incomplete combustion
• Carbon oxidises to carbon dioxide
• Hydrogen oxidises to water
• hydrocarbon + oxygen → carbon dioxide + water
Testing
for
carbon
dioxide
(CO
)
2
Testing for carbon dioxide (CO2)
• Carbon dioxide gas can be detected using
limewater
• Limewater turns cloudy white when carbon
dioxide is bubbled through it
Combustion in
in the
the laboratory
laboratory
Combustion
Incomplete combustion
combustion
Incomplete
• Occurs when the supply of oxygen is poor
• Water is still produced, but carbon monoxide and carbon
are produced instead of carbon dioxide
• Releases less energy than complete combustion
• hydrocarbon + oxygen → carbon monoxide + water
• hydrocarbon + oxygen → carbon + water
• Carbon monoxide is a toxic gas
• The carbon is released as soot
Carbon monoxide
monoxide
Carbon
• Carbon monoxide (CO) is a colourless,
odourless, toxic gas. It is poisonous
• It reduces the amount of oxygen that the
haemoglobin in the blood can carry around
the body
Carbon
(soot)
Soot
(carbon)
• Carbon, when deposited as soot, can collect
and block pipes. This can cause fires
• Soot particles can collect in the lungs, causing
lung diseases
• Discolours buildings
Which flame?
flame?
Which
Flame
Yellow
Blue
Collar Combustion
Closed Incomplete
Open
Yellow flame
produces soot
(carbon)
Complete
methane + oxygen →
carbon monoxide + water
OR
methane + oxygen →
carbon + water
methane + oxygen →
carbon dioxide + water
Blue flame
releases more
energy (more
efficient)
Sulphur dioxide
dioxide
Sulphur
• Sulphur dioxide (SO2) is produced when fuels
that contain impurities of sulphur burn
(oxidation)
• When SO2 dissolves in water droplets it makes
the rain more acidic than normal (acid rain)
Effects of
of acid
acid rain
rain
Effects
• Makes rivers, soils and lakes acidic- this harms
organisms living there
• Damages trees
• Speeds up the weathering of buildings made from
calcium carbonate
• Corrosion of metal
Global warming
warming
Global
• Gases (including carbon dioxide, methane and
water vapour) trap heat from the sun and
keep the Earth warm
• The Earth’s temperature varies
• Human activity may influence the
temperature of the Earth
Controlling the
the amount
amount of
of CO
CO22
Controlling
• The amount of CO2 in the atmosphere can be
controlled by:
- Iron seeding of oceans: addition of iron
compounds to encourage plant growth
(photosynthesis)
- Converting CO2 into hydrocarbons
The best
best fuel?
fuel?
The
• Factors to consider when choosing a fuel:
- How easily it burns
- Pollution e.g. acid rain, greenhouse effect (ash and
smoke)
- Energy value (J/g of fuel)
- Storage
- Transportation
The best
best fuel?
fuel?
The
• Solids are easier to store than liquids or gases
• Liquids and gases ignite more easily
• Liquids and gases flow (easily transported)
Fuel
Energy content (kJ/g)
mg of carbon dioxide
produced for each kJ
Natural gas
52
53
Petrol
43
71
Coal
24
93
• Coal releases the least amount of energy per gram of
fuel. It also produces the most carbon dioxide
• Carbon dioxide contributes to global warming
What are
are biofuels?
biofuels?
What
• Renewable fuels
• From the products of
living organisms
• Alternatives to fossil
fuels
Ethanol
Ethanol
• Ethanol is made by fermentation of sugar cane
or sugar beet
• Can be mixed with petrol for use as a fuel in
car engines
• Reduces the demand for petrol, conserving
crude oil supplies
• Carbon dioxide is made as a by-product
Advantages of
of biofuels
biofuels
Advantages
• Renewable resource
• Reduces the amount of carbon dioxide that
human activity puts into the atmosphere
(carbon neutral)
• Helps to reduce global warming
Disadvantages of
of biofuels
biofuels
Disadvantages
• Takes up valuable farming land
• Ethics of using food crops in this way, rather
than using them to feed hungry people
• Fossil fuels required to produce fertiliser for
the crops, harvest them, process them into
biofuels and transport the biofuels (so may
not be carbon neutral)
Hydrogen
Hydrogen
• An environmentally friendly alternative to
fossil fuels and biofuels
hydrogen + oxygen → water
2H2 + O2 → 2H2O
Problems with
with hydrogen
hydrogen
Problems
• Produced by passing electricity through water
(electricity generated using fossil fuels)
• Very flammable- may explode
• Must be compressed and chilled, then stored
in tough, insulated tanks
• Not as convenient as petrol and diesel