Topic 6 – National Chemistry Summary Notes
Fuels
Fuels and Combustion
LI 1
Coal, oil, gas and wood can all be used as fuels. These fuels have energy-rich
chemical bonds which were created using the energy from the SUN. The energy
is released when the fuel burns.
A FUEL is a substance which gives out ENERGY when it burns.
Any compound with STORED energy can be considered as a fuel.
When fuels burn they react with OXYGEN. This may also be referred to as
OXIDATION. Scientists use the word COMBUSTION to describe the process
of burning.
Combustion is an example of an exothermic reaction i.e. one which releases
energy.
e.g. the combustion of carbon:
C (s)
+ O2 (g)
CO2 (g)
(balanced)
An ENDOTHERMIC reaction is one in which energy is taken in.
LI 2
The Fire Triangle
The three things needed for burning are a fuel, oxygen and heat. These make up
the three sides of the fire triangle.
If you take away one side of the triangle, it will collapse. This means that if you
deprive a fire of either, fuel, oxygen or heat, then it will go out.
1
LI 3
Fossil Fuels
Coal, oil and natural gas are the three main fuels used in the UK today.
They are called the FOSSIL FUELS because they were formed from
once LIVING THINGS.
Fossil fuels such as oil and gas are examples of HYDROCARBON compounds
with minor impurities (coal is mostly just carbon). Hydrocarbons are compounds
made up of hydrogen and carbon only.
Even although there are large amounts of coal, oil and gas in the world today,
they will eventually run out. For this reason fossil fuels are called FINITE
resources because supplies are limited.
Formation of Coal
The formation of coal started around 300 million years ago. It is made from
dead plants and fern like trees that became buried in swampy land.
Pressure and temperature gradually made coal.
Formation of Oil & Natural Gas
Crude oil and natural gas came from microscopic sea animals and plants that
died and became covered by sediment. Again pressure and temperature over
millions of years changed the once living organisms into crude oil and natural gas.
Uses of Fossil Fuels
The fossil fuels are a useful reserve of fuels and are used to satisfy the
demands of an energy-dependent world e.g.

Electricity: The most common use of fossil fuels is the generation of electricity.
Fossil fuels like coal run most of the power plants in the world that generate
electricity.




Transportation: Most modes of transport are powered by coal and petrol.
Though hybrid and electric vehicles have made inroads into our lives, fossil fuels
still power millions of vehicles.
Industrial production: Fossil fuels, especially coal and oil, power most of the
industries throughout the world.
Kitchens: Nearly one-third of world's population uses fossil fuels like coal and
biomass, (such as wood and dung) for cooking and heating.
Heating: During winters, fossil fuels serve as excellent heat generators.
2
LI 4
Fractional Distillation of Crude Oil
The oil which comes out our oil wells is a black, sticky liquid with a very
unpleasant smell. It is called CRUDE OIL. It contains a rich mixture of valuable
chemicals called HYDROCARBONS.
The problem for chemists is how to separate the hydrocarbons in crude oil.
However, each hydrocarbon has its own BOILING POINT. If the crude oil is
slowly heated then each different hydrocarbon will boil and turn into a GAS at
different temperatures. The different gases can be collected separately. When
the gases cool they CONDENSE and turn into LIQUIDS. Each separate liquid is
called a FRACTION.A fraction is defined as a mixture of hydrocarbons with
similar boiling points. This whole process is called FRACTIONAL
DISTILLATION.
The first fractions which are obtained consist of GASES then they become
light coloured LIQUIDS and after that darker in colour liquids and thicker. The
final fraction which is left is known as BITUMEN RESIDUE and is the sticky
material used for building roads.
Fractional Distillation in the Lab
The set-up below shows how fractional distillation can be carried out in the lab.
3
The purpose of the air condenser is to cool the gases into liquids to allow for
collection.
The first fractions are volatile, light in colour, runny and highly flammable.
The later fractions are darker in colour, viscous and not so flammable.
definitions -
volatile
= evaporates easily
flammability = how easily a substance catches fire
viscosity
= how thick a liquid is
Fraction
Boiling
Range
(ºC)
Number of
Carbon
Atoms per
Molecule
Colour
Viscosity
Flammability
Speed of
Evaporation
Gases
-106–20
1 - 4
Gases
LOW
RUNNY
LIQUID
Catches fire
easily
FAST
Petrol
20 - 65
5 - 6
Clear, light
coloured liquid
Naphtha
65 - 180
6 - 11
Pale yellow
Kerosene
(paraffin)
180–250
9 – 15
Gas oils
(diesel)
250–350
15 – 25
Catches fire
with difficulty
Dark yellow
HIGHLY
VISCOUS
Residue
> 350
> 25
Dark Brown
4
(very thick)
Does not
catch
fire
SLOW
Uses of Fractions
FRACTION
USE
Refinery Gas
Cooking, heating
Petrol
Car fuel
Naphtha
Chemicals e.g. plastics, solvents
Kerosene
Jet fuel
Diesel (gas oils)
Heavy transport, some cars
Lubricating oils
Engine oil, candle wax
Bitumen
Building roads, roofing
The following saying can help us to remember the order and names of the
fractions obtained from the fractional distillation of crude oil.
Giant Planes Need Kerosine During Our Boarding
G
A
S
E
S
P
E
T
R
O
L
N
A
P
T
H
A
K
E
R
O
S
I
N
E
D
I
E
S
E
L
5
O
I
L
S
B
I
T
U
M
E
N
Fractional Distillation in Industry
Liquefied petroleum
gas
Chemicals
Fractions
decreasing in
density and
boiling point
Petrol for vehicles
Jet fuel, paraffin
for heating and
lighting
Diesel fuels
Crude oil
Lubricating oils,
waxes and polishes
Fuels for
ships,
factories
and central
heating
Fractions
increasing
in density
and
boiling
point
Bitumen for roads
and roofing
6
LI 5
Properties of Crude Oil Fractions
The fractions obtained from crude oil have different properties because they
contain hydrocarbons of different sizes. The simplest way to think about the
size of a hydrocarbon is to count the number of carbon atoms in the molecule.
a) Boiling Points
The first fractions that are distilled have low boiling points. This is because
they consist of small molecules.
There are small forces of attraction that exist between molecules. These
forces are bigger and stronger for large molecules. It takes more energy to
separate large molecules and therefore larger molecules have higher boiling
points.
b) Viscosity (thickness)
The fractions containing bigger molecules have a higher viscosity. This is
because they are made of long chains of atoms which tend to get tangled up and
clump together.
c) Flammability
Small hydrocarbons are more flammable than larger molecules i.e. they catch
fire more easily. This is because small molecules can react more quickly with
oxygen in the air.
d) Ease of Evaporation
Small molecules evaporate more easily than larger molecules since they have
much lower boiling points.
7
LI 6
Combustion of a Hydrocarbon
This apparatus can be used to show the combustion products of a hydrocarbon.
The burning wax candle produces gases which are drawn through the apparatus
by the pump.
u-tube
Results
1. The limewater turns milky indicating the presence of carbon dioxide gas.
2. The drops of condensation in the u-tube boil at 100ºC and freeze at 0⁰C. This
indicates the presence of water.
Complete Combustion
hydrocarbon
+
oxygen
carbon dioxide
+ water
e.g. complete combustion of methane gas - CH4
CH4 (g) +
CH4 (g)
O2 (g)
+ 2O2 (g)
CO2 (g)
+
H2O (l)
CO2 (g)
+ 2H2O (l)
(unbalanced)
(balanced)
Hydrocarbons burn in a plentiful supply of oxygen to produce
CARBON DIOXIDE and WATER. This is called
COMPLETE COMBUSTION.
8
LI 7
Incomplete combustion
Often when a fuel burns there is not enough oxygen to produce carbon dioxide
gas (CO2). Instead, the gas carbon monoxide, (CO) is formed. Carbon monoxide
is a poisonous gas. In large amounts it can kill by destroying the blood’s ability
to carry oxygen.
hydrocarbon
+
limited
oxygen
carbon monoxide
+ water
In a limited supply of oxygen, hydrocarbons burn to produce
carbon monoxide gas. This is called INCOMPLETE COMBUSTION.
LI 8
Catalytic Converters
In car engines, catalytic converters can be used to minimise the output of
carbon monoxide. This device fits on to the exhausts of cars and converts
harmful gases into harmless ones.
However, they have no beneficial effect on carbon dioxide levels which
contribute to GLOBAL WARMING.
Fuels and Pollution
LI 9
POLLUTANT
Carbon monoxide
Sulphur dioxide
Hydrocarbons
Oxides of nitrogen (NOx)
Lead compounds
MAIN SOURCE
EFFECT
Vehicle engines and
industry
Burning fossil fuels in
power stations
Burning fuels in vehicles
and factories
Vehicle engines
Poisonous
Used to be added to
petrol to make it burn
more smoothly
Toxic and can cause brain
damage
9
Forms acid rain
Irritating, toxic
compounds formed in air
Forms acid rain
LI 10
Global Warming and the Greenhouse Effect
The increasing level of carbon dioxide in the atmosphere is a cause for concern.
As the amount of carbon dioxide in the atmosphere increases more of the suns
energy is retained. This causes the average temperature of the earth’s surface
to rise. This is known as the GREENHOUSE EFECT. Scientists still argue about
the effect this will have but it is thought some parts of the world will warm up
by around 4⁰C whilst other parts may cool down. This may well cause flooding in
certain areas due to an increase in the levels of rivers and seas.
Burning fuels for heating, for cars and other vehicles and for making electricity
in power stations all produces carbon dioxide which adds to the greenhouse
effect.
How much CO2 does
your lifestyle emit
each year?
10
LI 11
Reducing Carbon Dioxide Emissions
Alternative Energy Sources
Fossil fuels are in short supply and will eventually run out, for this reason they
are called NON RENEWABLE sources of energy.
Other methods of generating electricity need to be developed. These include
using the sun’s energy, wind, water and wave action. These methods provide an
unlimited supply and they will not run out. They are called RENEWABLE or
ALTERNATIVE ENERGY sources.
RENEWABLE
ENERGY
SOURCE
ADVANTAGES
Hydroelectric
Solar
Wind
Wave
11
DISADVANTAGES
Biofuels
Biofuels are considered a viable alternative to fossil fuels.
Many different varieties exist and they vary significantly.
All biofuels and bio-based products come from “biomass”, a term that covers all
living or recently living biological material which can be used as fuel or for
industrial production.
Examples include wood, corn, sugarcane, and manure.
Biofuels can be separated into three basic categories:
A. ETHANOL: primarily used in cars, ethanol is a type of alcohol and is most
commonly made from corn or sugarcane.
B. BIODIESEL: a substitute for diesel fuel, which is used mostly in lorries and
trucks but also in an increasing number of diesel cars. Most commonly made
from soybeans.
C. OTHER BIOMASS: mostly used for generation of electricity or heat.
Examples: burning wood chips to boil water and create steam, which spins
turbines and creates electricity; collecting methane from manure piles to
generate heat or electricity
BIOFUELS
ADVANTAGES
Made from renewable sources so will
not run out
Safer for the environment if they get
spilled
DISADVANTAGES
Land not always available to grow crops
Less pollution compared to regular
fuels
Some biofuels are more corrosive than
petrol and damage engines
Decreased access to food
Cheaper than regular fuels since plants
are cheaper than oil
Do not contribute to increased levels
of CO2.
12
LI 12
Carbon Capture
Carbon capture and storage (CCS) is the process of capturing waste carbon
dioxide (CO2) from large point sources, such as fossil fuel power plants,
transporting it to a storage site, and depositing it where it will not enter the
atmosphere, normally deep underground.
The aim is to prevent the release of large quantities of CO2 into the atmosphere
from fossil fuel use in power generation and other industries.
Although CO2 has been injected into geological formations for several decades
for various purposes, the long term storage of CO2 is a relatively new concept.
13
Topic 6 Pupil Self Evaluation
Number
Learning Intention
1
I will found out about fuels and combustion
2
I will find out what makes up the three
sides of the fire triangle
3
4
I will find out about the fossil fuels, how
they were formed and their uses
I will find out how crude oil is separated
into different fractions by the process of
fractional distillation
Success Criteria
I can:






I can:


I can:




State the definition of a fuel
Give examples of fuels
State that energy is released when fuels burn
State that combustion is an exothermic reaction
Write a combustion word/formula equation
Define the terms exothermic and endothermic
Draw the fire triangle
State what happens when one side of the fire triangle is
removed
State the three fossil fuels are coal, oil and natural gas
Describe the formation of the fossil fuels
State that the fossil fuels are finite resources
State that oil and gas are hydrocarbon compounds with minor
impurities.
Give examples of uses of the fossil fuels

I can:
 Describe how hydrocarbons in crude oil are separated by their
difference in boiling point.
14



Describe how fractional distillation is carried out in the lab and
in industry
State the names of the different fractions
Give uses for fractions
5
I will find out about the properties of the
different fractions obtained from crude oil
I can:
 Describe the different properties of fractions in terms of
carbon chain length, colour, viscosity, flammability and ease of
evaporation
 Explain why properties of fractions change as molecules increase
in size
6
I will find out what the combustion products
of a hydrocarbon are by experimentation
7
I will find out what the products of
incomplete combustion of a hydrocarbon are
8
I will find out the purpose of fitting
catalytic converters to cars
I can:
 State the products of complete combustion of a hydrocarbon as
carbon dioxide and water
 Describe the chemical test for carbon dioxide and water
 Write a formula/word equation for complete combustion of a
hydrocarbon
I can:
 State that carbon monoxide and water are the products of
incomplete combustion of a hydrocarbon
 State that carbon monoxide is a poisonous gas
 Describe the effect carbon monoxide has on the body
I can:
 State that catalytic converters change harmful gases into
harmless gases
15

9
I will find out about pollutants, their
sources and environmental effects
10
I will find out about global warming and its
environmental effects
11
I will find out about alternative energy
sources including biofuels
12
I will find out about carbon capture
State that fitting a catalytic converter does not have a
beneficial effect on carbon dioxide levels in the atmosphere.
I can:
 Give examples of pollutants from fuels
 State the source of the pollutant and describe its effect on the
environment and our health
I can:
 Explain why the temperature of the earth is increasing
 Give examples of the effects of global warming
I can:
 Give examples of renewable energy
 State advantages and disadvantages of renewable energy
I can:
 Describe what is meant by carbon capture
 Explain why this would be beneficial to the environment
16