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Topic 6 – National Chemistry Summary Notes

Fuels

Fuels and Combustion

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.

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.

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.

A FUEL is a substance which gives out ENERGY when it burns.

Any compound with STORED energy can be considered as a fuel.

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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.

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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.

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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 =

flammability =

viscosity =

evaporates easily

how easily a substance catches fire

how thick a liquid is

Fraction Boiling

Range

(ºC)

Number of

Carbon

Atoms per

Molecule

Colour Viscosity Flammability Speed of

Evaporation

Gases

Petrol

Naphtha

Kerosene (paraffin)

Gas oils (diesel)

Residue

-106–20

20 - 65

65 - 180

180–250

250–350

> 350

1 - 4

5 - 6

6 - 11

9 – 15

15 – 25

> 25

Gases

Clear, light coloured liquid

Pale yellow

Dark yellow

Dark Brown

LOW

RUNNY LIQUID

HIGHLY VISCOUS

(very thick)

Catches fire

easily

Catches fire with difficulty

Does not

catch fire

FAST

SLOW

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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

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Liquefied petroleum

gas

Chemicals

Petrol for vehicles

Jet fuel, paraffin

for heating and

lighting

Diesel fuels

Lubricating oils,

waxes and polishes

Fuels for

ships,

factories

and central

heating

Bitumen for roads

and roofing

Fractions

decreasing in

density and

boiling point

Crude oil

Fractions

increasing

in density

and

boiling

point

Fractional Distillation in Industry

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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.

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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.

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) + O2 (g) CO2 (g) + H2O (l) (unbalanced)

CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (l) (balanced)

Hydrocarbons burn in a plentiful supply of oxygen to produce

CARBON DIOXIDE and WATER. This is called

COMPLETE COMBUSTION.

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u-tube

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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 carbon monoxide + water

oxygen

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

POLLUTANT

MAIN SOURCE EFFECT

Carbon monoxide Vehicle engines and

industry

Poisonous

Sulphur dioxide Burning fossil fuels in

power stations

Forms acid rain

Hydrocarbons Burning fuels in vehicles

and factories

Irritating, toxic

compounds formed in air

Oxides of nitrogen (NOx)

Vehicle engines Forms acid rain

Lead compounds

Used to be added to

petrol to make it burn

more smoothly

Toxic and can cause brain

damage

In a limited supply of oxygen, hydrocarbons burn to produce

carbon monoxide gas. This is called INCOMPLETE COMBUSTION.

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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?

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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

DISADVANTAGES

Hydroelectric

Solar

Wind

Wave

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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 DISADVANTAGES

Made from renewable sources so will

not run out

Land not always available to grow crops

Safer for the environment if they get

spilled

Decreased access to food

Less pollution compared to regular

fuels

Some biofuels are more corrosive than

petrol and damage engines

Cheaper than regular fuels since plants

are cheaper than oil

Do not contribute to increased levels

of CO2.

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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.

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Topic 6 Pupil Self Evaluation

Number

Learning Intention

Success Criteria

1 I will found out about fuels and combustion 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

2 I will find out what makes up the three

sides of the fire triangle

I can:

Draw the fire triangle

State what happens when one side of the fire triangle is

removed

3 I will find out about the fossil fuels, how

they were formed and their uses

I can:

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

4 I will find out how crude oil is separated

into different fractions by the process of

fractional distillation

I can:

Describe how hydrocarbons in crude oil are separated by their

difference in boiling point.

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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

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

7 I will find out what the products of

incomplete combustion of a hydrocarbon are

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

8 I will find out the purpose of fitting

catalytic converters to cars

I can:

State that catalytic converters change harmful gases into

harmless gases

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State that fitting a catalytic converter does not have a

beneficial effect on carbon dioxide levels in the atmosphere.

9 I will find out about pollutants, their

sources and environmental effects

I can:

Give examples of pollutants from fuels

State the source of the pollutant and describe its effect on the

environment and our health

10 I will find out about global warming and its

environmental effects

I can:

Explain why the temperature of the earth is increasing

Give examples of the effects of global warming

11 I will find out about alternative energy

sources including biofuels

I can:

Give examples of renewable energy

State advantages and disadvantages of renewable energy

12 I will find out about carbon capture I can:

Describe what is meant by carbon capture

Explain why this would be beneficial to the environment