NATIONAL 3
Fuels and Combustion
Fuels are chemicals which burn, giving out energy.
The gas oxygen is used up in the process.
A reaction in which oxygen is used up as energy is released is known as a combustion
reaction.
Fighting fires
A fire needs a fuel, oxygen (usually from the air) and a temperature high enough to start the
fire and keep it going.
The three 'ingredients' necessary for fire are shown in the 'fire triangle' on the right.
If one of these 'ingredients' is taken away, from a fire, it will
go out.
Removing heat from a fire
Heat can be removed from a fire by spraying water on it. The water cools the fire down and
puts the fire out.
Water must not be used with oil, petrol and electrical fires.
Removing oxygen from a fire
This is normally done by smothering the fire. Options include:




Wrapping a fire blanket around a person whose clothes are on fire
Placing a damp cloth over a burning chip pan
Using a fire extinguisher containing carbon dioxide or foam
Using sand
Removing fuel from a fire
Gas fires and Bunsen burners go out when the gas supply is turned off.
Estimates of how long they will last
Fossil fuels
These are fuels made from material that was once living. There are three common fossil fuels
- Coal, oil and natural gas. Peat can also be described as a fossil fuel.
These fuels will not last for ever - they are finite resources.
Origin of Fossil Fuels
Coal is made from fern-like trees that became buried in swampy land over 350 million years
ago.
This material was squashed (pressure) and heated and over a period of millions of years
gradually formed coal.
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.
These are both mined from the land or under the sea.
Pollution from Coal and Oil
 Coal mining leaves scars
on the environment and coal
bings alter the shape of the
landscape.
 Oil spillage can cause
serious damage to marine life.
 Fossil fuels also damage
the environment when they are burned as they produce acidic and greenhouse gases.
Burning fossil fuels
Oil fractions are mainly hydrocarbons - compounds containing only hydrogen and carbon.
When these burn in air, carbon dioxide and water are formed. This can be shown using the
following experiment.


Carbon dioxide turns limewater milky (cloudy).
Water is best identified by measuring its freezing and boiling point and confirming
they are the same as that of pure water, but can also be identified using cobalt chloride
paper which changes from blue to pink when water is present. If the middle test tube
is cooled by placing it in ice, condensation (water) would be seen forming on the
inside of the tube. Water also has a pH of 7.
When we burn methane (natural gas) in a Bunsen burner it also produces carbon dioxide and
water. This can be seen if we place a boiling tube into the flame for a few seconds, droplets
of water are deposited on the outside of the tube. If the tube is held there too long, the tube
becomes too warm for the water to remain as a liquid and the condensation disappears.
It the mouth of the test tube is held near the flame horizontally for a few seconds (to attempt
to 'catch some of the gases being formed) and then lime water is added to the tube, it will turn
cloudy. This proves carbon dioxide is being produced.
Pollution problems resulting from burning fossil fuels
A. Carbon dioxide - This gas causes global warming (greenhouse effect).
B. Carbon monoxide - This gas is made when fuels containing carbon burn in
insufficient air or oxygen.
Carbon monoxide is very poisonous and
especially dangerous
because it is colourless, odourless and
tasteless.
C. Sulphur dioxide - If sulphur is present in a
fuel, sulphur dioxide is
made when it burns.
Sulphur dioxide, a
poisonous gas, causes acid rain and can trigger
asthma.
Sulphur is often removed from fuels before they are burned so
that pollution is reduced.
D. Nitrogen oxides - Fuels
need oxygen from the air to
burn. In petrol engines, the
spark provides the activation
energy to ignite the fuel. Unfortunately the
spark can also cause nitrogen and oxygen
molecule to combine to make nitrogen oxides.
These are poisonous
gases which add to the acid rain problem. The
same gases are formed
when a lightning bolt passes through the air.
Renewable energy sources
Renewable energy sources are energy sources that will not run out and can be replaced. These
can be alternative fuels or harnessing energy from natural resources.
Most of the world's energy currently comes from burning fossil fuels. This not only uses
finite resources (they will run out), but also produces greenhouse gases such as carbon
dioxide and acidic gases such as sulphur dioxide.
The fact that one day fossil fuels will run out and burning them produces unwanted gases, we
have no choice but to consider alternative, renewable energy sources.
Wind energy
Wind energy can be harnessed by large wind turbines. The wind turns the blades of the
turbines which then produces an electric current (transforming movement energy into
electrical energy).
This provides a free source of electricity, but does rely on the wind and there is an ongoing
debate about the locations of these farms, which some argue spoil areas of natural beauty.
Hydroelectricity
Water stored in high reservoirs can flow through tunnels and turn the blades of a turbines
which then produces an electric current (transforming stored gravitational potential energy
into movement energy and then into electrical energy).
This provides a free source of electricity, but does rely on the water being stored in
reservoirs.
The power station at Ben Cruachan in Scotland can also pump water back into the reservoir
when there is surplus electricity (this is a useful way of storing this energy).
The generators (and entire power station) at Ben Cruachan are actually inside the mountain. It
is known as the 'hollow mountain'.
Due to its many moutains and resevoirs, Scotland is an ideal location for hydroelectric power
stations.
Wave energy
Energy can be harnessed from waves by placing special wave energy machines into the sea.
The machines float near the surface of the water and move up and down as the waves pass
by.
As with many methods of generating electrical energy, movement energy is transformed into
electrical energy.
Solar
energy
Energy directly from the sun can be used to provide energy.
This concept is nothing new as plants have been doing this well before man ever thought
about it!
The heat energy from the sun can be used directly to heat objects using a solar furnace. This
equipment focuses the suns rays on a single point (in the same way a satellite dish works.
Large solar furnaces can easily melt metals!
Many houses invest in solar heating panels that use the energy from the sun to heat water or
other refrigerants.
Light energy from the sun can also be converted to electrical energy using a photovoltaic cell.
Solar panels made from these cells can be used to generate free electricity for a typical
household. The downside with these solar panels is that they do not work at night!
There are other panels, such as thermodynamic panels that can absorb sunlight energy and
heat energy from the air around them (which has been warmed by the sun). These panels can
still work after the sun has set!
Biogas
Methane is found in biogas which can be generated by the decomposition of waste plant
material (biomass). This process also takes place inside the gut of animals.
Cows in particular produce large volumes of methane gas. Methane gas is also a greenhouse
gas.
Biogas produces carbon dioxide and water when it burns.
Biodiesel
Biodiesel can be made from natural oils such as sunflower and vegetable oil. Since these are
renewable sources, biodiesel is a renewable fuel. However, if vegetables and plants are used
to make biodiesel, this may have serious implications for the world's food supply.
When it burns it produces carbon dioxide (and water), which can contribute to global
warming.
Bioethanol
Ethanol (a common type of alcohol) is made from sugar cane by a process called
fermentation. This biological process uses enzymes found in yeast.
This bioethanol can be extracted and mixed with petrol to make a fuel for cars.
As sugar cane is renewable, alcohol as a fuel is renewable. However, if sugar (or sugary
crops) is used to make bioethanol, this may have serious implications for the world's food
supply. Scotland used to produce sugar beet which could have been converted to bioethanol.
As fossil fuels run out, this may happen again.
Alcohol burns readily and can produce an explosion when a small quantity of alcohol vapour
and air are ignited with a spark - your teacher may demonstrate this.
Bioethanol produces carbon dioxide and water when it burns.
Hydrogen
Hydrogen is the most abundant element in the universe and our sun's energy comes from a
nuclear reaction using hydrogen as a fuel.
On earth hydrogen is joined up to oxygen in the compound water (H2O)
Electricity can be used to break apart water into the separate elements hydrogen and oxygen.
This process is called electrolysis. Hydrogen, which can be obtained from water, is a likely
fuel for the future, especially if the electricity can be generated from renewable sources.
water
hydrogen + oxygen
One of the major benefits of using hydrogen as an alternative fuels is that it only produces
water when it burns. This makes it a clean burning fuel which can be used in an internal
combustion engine (car engine) or reacted with oxygen in a hydrogen fuel cell to provide
electricity.
Hydrogen is seen as a means of storing energy (from the sun) and a means of distributing
energy. However, since it is an extremely explosive gas, carefully consideration must be
made as to how it is stored and used.
The test for hydrogen is that it burns with a squeaky pop.
New words and their meanings
Fuel - A chemical that can release energy.
Combustion - The reaction of a fuel with oxygen to release energy.
Fossil fuels - Coal, oil and natural gas are fuels that are made from fossilised materials and
can be burned to release energy.
Finite resources - Something that will run out and will not last forever.
Renewable resources - Something that will not run out.
Greenhouse gases - A gas that causes the Earth to traps the sun's energy more than normal.
This can cause the Earth to warm.
Global warming - The warming of the planet which may be caused by greenhouse gases.
Pollution - Substances which damage the environment
Fractional distillation - Separation of a mixture of substances into parts or fractions based the
fact that they have different boiling points
Hydrocarbons - The name given to compounds entirely made up of the elements carbon and
hydrogen.
Catalytic converter - A device fitted to cars that changes harmful exhaust gases into less
harmful ones.
Wind energy - A renewable source of energy. Wind causes turbine blades to move and this
movement energy is converted to electrical energy.
Hydroelectricity - A renewable source of energy. Fast flowing water causes turbine blades to
move and this movement energy is converted to electrical energy.
Wave energy - A renewable source of energy. Waves cause floats to move up and down and
this movement energy is converted to electrical energy.
Solar energy - A renewable source of energy from the sun. This energy can be used to heat
directly or generate electrical energy.
Biomass - Organic material (plant and animal waste) that can be used to produce biofuels
such as biogas, biodiesel and bioethanol.
Biogas - A renewable fuel made from decaying organic material. Methane is the main
chemical in biogas.
Biodiesel - A renewable fuel made by chemically changing oils (and fats) from natural
sources.
Bioethanol - A renewable fuel made by fermenting sugar using enzymes found in yeast.
Bioethanol is made of the chemical called ethanol which is a type of alcohol.
Hydrogen - A renewable fuel made by breaking up water using electricity.
Electrolysis - Using electricity to break up a compound.
NATIONAL 4
Fuels.
Fuels are chemicals which have stored energy. This energy can be released when they burn in
oxygen.
A reaction in which oxygen is used up as energy is released from a fuel is known as
oxidation. The most common version of oxidation is burning, which is properly called
combustion. Combustion is therefore an exothermic reaction.
The energy that is stored in fuels comes from bonds between atoms.
Plants are capable of making their own food
(which is a fuel) by taking in carbon dioxide and water to make glucose and oxygen in a
process called photosynthesis. This uses and stores energy from the sun into the food.
When animals (including us) eat plants, this energy is released during respiration - the
process of obtaining energy from food. Our bodies can also store the food and keep the
energy for later.
Fossil fuels (from plants) such as coal, peat, oil, natural gase and other plant based fuels such
as wood and biomass have this energy trapped inside, making them useful fuels.
Fighting fires
A fire needs a fuel, oxygen (usually from the air) and a temperature high enough to start the
fire and keep it going.
The three 'ingredients' necessary for fire are shown in the 'fire triangle' on the right.
If one of these 'ingredients' is taken away, from a fire, it will
go out.
Removing heat from a fire
Heat can be removed from a fire by spraying water on it. The water cools the fire down and
puts the fire out.
Water must not be used with oil, petrol and electrical fires.
Removing oxygen from a fire
This is normally done by smothering the fire. Options include:




Wrapping a fire blanket around a person whose clothes are on fire
Placing a damp cloth over a burning chip pan
Using a fire extinguisher containing carbon dioxide or foam
Using sand
Removing fuel from a fire
Gas fires and Bunsen burners go out when the gas supply is turned off.
Estimates of how long they will last
Fossil fuels
These are fuels made from material that was once living. There are three common fossil fuels
- Coal, oil and natural gas. Peat can also be described as a fossil fuel. These fuels play a
major role in the world's economy.
These fuels will not last for ever - they are finite resources.
Coal is made from fern-like trees that became buried in swampy land over 350 million years
ago.
This material was squashed (pressure) and heated and over a period of millions of years
gradually formed coal.
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.
These are both mined from the land or under the sea.
Burning fossil fuels
Fossil fuels are mainly hydrocarbon compounds (compounds containing only hydrogen and
carbon). They also contain other impurities.
Crude oil is a mixture of hydrocarbons which are similar to each other in chemical makeup
and chemical properties, but differ in size of molecule.
When these burn in a plentiful supply of air (or oxygen), carbon dioxide and water are
formed. This can be shown using the following experiment.


Carbon dioxide turns limewater milky (cloudy).
Water is best identified by measuring its freezing and boiling point and confirming
they are the same as that of pure water, but can also be identified using cobalt chloride
paper which changes from blue to pink when water is present. If the middle test tube
is cooled by placing it in ice, condensation (water) would be seen forming on the
inside of the tube. Water also has a pH of 7.
When we burn methane (natural gas) in a Bunsen burner it also produces carbon dioxide and
water. This can be seen if we place a boiling tube into the flame for a few seconds, droplets
of water are deposited on the outside of the tube. If the tube is held there too long, the tube
becomes too warm for the water to remain as a liquid and the condensation disappears.
It the mouth of the test tube is held near the flame horizontally for a few seconds (to attempt
to 'catch some of the gases being formed) and then lime water is added to the tube, it will turn
cloudy. This proves carbon dioxide is being produced.
If the air-hole on a Bunsen burner is closed, it reveals the 'safety flame'. This flame isn't as
hot as a blue flame and it is also visible, making it safer than a blue flame. If glassware is
heated in this yellow flame, it becomes covered in soot (carbon).
When fossil fuels burn in a limited supply of oxygen, they can also produce carbon monoxide
and carbon.


Carbon monoxide is a particularly poisonous gas that has has no taste or smell. It
permanently joins with haemoglobin in our red blood cells making them unable to
carry oxygen around our bodies.
Carbon particles can be harmful to our health as the particles can collect in our lungs.
Reducing pollution from car engines
A special exhaust system called a catalytic converter was introduced in the UK in 1991. This
reduced the quantities of harmful gases such as carbon monoxide and unburnt hydrocarbons
as well as nitrogen oxides, by changing them into less harmful gases such as and carbon
dioxide, water and nitrogen.
Catalytic converters contain expensive metals such as platinum.
The expensive metals are spread thinly over a ceramic honeycomb so that they have a large
surface area to react with the harmful gases.
The carbon cycle
The element carbon plays an important role in our environment. This can be shown in a
simplified version of the carbon cycle below. This shows the different forms that carbon can
exist in and how it moves through the environment.
Burning fuels containing carbon produces carbon dioxide (pollution) which can impact on the
carbon cycle, particularly in the formation of acid rain and ocean acidification.
Reducing the production or release of excess carbon dioxide is important in maintaining a
balance in the carbon cycle.


Carbon dioxide emissions can be reduced by burning less fossil fuels.
Carbon capture schemes which remove carbon dioxide gases from the gases released
by power plants. This can then be stored or used in other chemical processes.
Biofuels from biomass
Biomass is a term that describes most organic material (from living origin). This can include
waste plant and animal material and oils, sugars and other materials made directly from
plants.
Biomass can be burned as a fuel directly, but often it is converted into other biofuels
Because biomass is renewable, biofuels made from this are also renewable.
Renewable energy sources are energy sources that will not run out and can be replaced. These
can be alternative fuels or harnessing energy from natural resources. Some examples of
biofuels are given below.
Biogas
Methane is found in biogas which can be generated by the decomposition of waste plant
material. This process also takes place inside the gut of animals.
Cows in particular produce large volumes of methane gas. Methane gas is also a greenhouse
gas.
Biogas produces carbon dioxide and water when it burns.
Biodiesel
Biodiesel can be made from natural oils such as sunflower and vegetable oil. Since these are
renewable sources, biodiesel is a renewable fuel. However, if vegetables and plants are used
to make biodiesel, this may have serious implications for the world's food supply.
When it burns it produces carbon dioxide (and water), which can contribute to global
warming.
Bioethanol
Ethanol (a common type of alcohol) is made from sugar cane by a process called
fermentation. This biological process uses enzymes found in yeast.
This bioethanol can be extracted and mixed with petrol to make a fuel for cars.
As sugar cane is renewable, alcohol as a fuel is renewable. However, if sugar (or sugary
crops) is used to make bioethanol, this may have serious implications for the world's food
supply. Scotland used to produce sugar beet which could have been converted to bioethanol.
As fossil fuels run out, this may happen again.
Alcohol burns readily and can produce an explosion when a small quantity of alcohol vapour
and air are ignited with a spark - your teacher may demonstrate this.
Bioethanol produces carbon dioxide and water when it burns.
//KEYWORDS AT THE BOTTOM
New words and their meanings
Fuel - A chemical that has stored energy which can be released
Oxidation - The reaction of a chemical with oxygen.
Burning - The common name for a fuel reacting with oxygen.
Combustion - An alternative word to burning.
Exothermic - A reaction that releases energy (heat, light, etc.).
Photosynthesis - The process by which plants make food using carbon dioxide and water.
They store energy in the bonds within the molecules of food. The food produced can be
classed as a fuel.
Respiration - The process of releasing energy from food within our cells.
Biomass - Organic/living/plant material. Biomass can be converted into various biofuels, or
used as a fuel directly.
Fire triangle - Removing heat, oxygen or fuel from a fire will put the fire out.
Finite resource - Something we use that will run out (will not last forever). Fossil fuels are
finite resources.
Hydrocarbon - A compound made from the elements carbon and hydrogen only.
Fractional distillation - The process of separating the mixture of hydrocarbons in crude oil.
This process works on the fact that the different hydrocarbon molecules in crude oil have
different boiling points.
Catalytic converter - A device fitted to cars to reduce the pollution from car emissions.
Biofuel - A fuel made from biomass.
Renewable - Something that will not run out, or can be replaced.