C.1.

Energy Sources
 ENERGY

• Energy is defined as the ability to do work.

• The Law of Conservation of Energy states that energy
can neither be created nor destroyed. It can only be
converted from one form to another.
• The “quality” of our energy is being degraded as it is
transferred from one form to another.
• Energy and materials go from a concentrated into a
dispersed form.
• If we lose energy to the environment, it is no longer
available to do useful work.

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C.1. Energy sources
• An energy source needs to be cheap, plentiful, and
readily accessible and provide high-quality energy at
a suitable rate – not too fast or too slow.
• A fuel is a substance that can release energy by
changing its chemical or nuclear structure.

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Renewable and Non-renewable Energy
• A renewable source of energy is one that is
replenished at a greater rate than it is used up.
• Hydroelectric dam – replenished by rainfall
• Wood for fuel – replaced by growing trees
• Solar and wind energy
• fuel cells/biomass/geothermal

• A non-renewable source of energy is one that is not

replenished as it is used up. Examples, fossil fuels.
• Coal – millions of years for fossil fuels to form
• Oil
• Natural gas

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Energy density and specific energy

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Comparison of energy sources

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Example
 The enthalpies of combustion of a range of organic
compounds are given in the IB Data Booklet.
 Calculate the specific energy and energy density of
hexane from its density which is 0.6548 g/cm3 under
standard conditions.
 Information needed:
1. Formulas for compound and formulas for specific
energy & energy density found in IB Data Booklet.
2. Molar mass
3. Heat of combustion from IB Data Booklet

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Solution
 Hexane is C6H14 with a molar mass of 86.2 g/mol.
 It’s enthalpy of combustion is -4163 kJ/mol.
 We are given the density of 0.6548 g/cm3.
Energy Released
SpecificEnergy=
Mass of fuel
 We have to use the correct units.
 From the formula the unit of energy density = kJ/g.
 How do we get these units from the given
information?

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Calculation
 If we divide the enthalpy of combustion by the molar
mass, we will have the correct units.
-4163kJmol -1 -1
=43.2kJg
83.2gmol -1
Thus, the specific energy is 43.2kJ/g
Calculation of Energy density
Energy Released
Energy Density =
Volume of fuel
 From above, we need kJ/cm3 so multiply the specific
energy by the density to get the energy density.
 48.3kJ/g x 0.6548g/cm3 = 31.6 kJ/cm3

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Try 1
 The standard enthalpy of combustion of carbon is -
394kJ/mol. The density of anthracite, one of the purest
coals, is 2267kg/m3.
 Use this information to calculate the energy density
and specific energy of this form of coal.

 Answers
 Specific energy = 32.8 kJ/g
 Energy density = 7.44 x 107 kJ/m3

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Try 2
 Ethanol is a fuel produced from plant products by
fermentation. It has a density of 789 g/dm3 and its
enthalpy of combustion is -1367 kJ/mol.
 Calculate energy density and specific energy.
 Write a balanced equation for the combustion of
ethanol and state the amount, in mol, of carbon
dioxide produced per mole of ethanol burned.
 Why is this considered “green or renewable” fuel even
though it produces CO2 in the combustion reaction.

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Try 3
 The enthalpies of combustion of methane and
hydrogen are given in section the IB data booklet.
 a). Calculate the specific energies of CH4 and H2.
 b). Use the ideal gas equation to calculate the density
of the two gases at STP and hence calculate the
energy density of the two gases.
 c). Identify the best fuel based on this information and
discuss the practical difficulties involved in its
widespread use.

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Choice of fuel based on energy
density and specific energy
• Nuclear fuels have the highest specific energies
followed by fossil fuels which are higher than
renewable sources.
• The higher the specific energy, the better the fuel
source, but this has to be balanced with renewable vs
non-renewable considerations.

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Example

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Effciency of energy transfer

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Example
 A coal-burning power station generates electrical
power at a rate of 5.50 x 108 J/s.The power station has
an overall efficiency of 36% for the conversion of heat
into electricity.
 a. Calculate the total quantity of electrical energy
generated in one year of operation.
 b. Calculate the total quantity of heat energy used in
the generation of this amount of electricity.
 c. Calculate the mass of coal that will be burned in one
year of operation, assuming that coal has the enthalpy
of combustion of graphite.

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Solution
You need the formula:

Useful Energy
Energy Efficiency = x100
Total Energy Input Energy

 Data;
 Efficiency = 36% and rate = 5.50 x 108 J/s
 Enthalpy of combustion = -394 kJ/mol
a) Energy in one year:
 5.50 x 108 J/s x 60s/min x 60 min/hr x 24 hr/day x 365
days/yr = 1.73 x 1016 J

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Solution continued
 b)
Useful Energy
Efficiency = x100=36%
Total Energy Input Energy

 Useful output energy = 36%

 The calculated output energy in “a” is 1.73x1016J
 Therefore the total input energy can be obtained:

1.73x1016 J
Input Energy = x100=4.82x1016
36

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Solution continued
 c) Heat energy = 4.82 x 1016 J = 4.82 x 1013 kJ

 To solve for moles, use the enthalpy of combustion.

 1 mole produces 394kJ, therefore how many moles will
produce 4.82x1013kJ?
4.82x1013kJ 11
= -1
=1.22x10 moles
394kJmol
 To solve for mass, multiply by the molar mass.

 1.22 x 1011 mol x 12.01 g/mol = 1.47 x 1012 g

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Try
 4.00 x 107 kJ are required to heat a home in a typical
winter month.
 a.The house can be heated directly with a gas boiler
burning methane gas (efficiency 85%). Calculate the
mass of methane required in one month using this
method of heating.
 b.The home can also be heated using electricity from
a natural gas-burning power plant (efficiency 50%).
Determine the mass of methane needed to generate
the electricity needed to heat the house in a month.
 *Note that the input energy must be larger than the
output energy. Use this rule of thumb when using the
efficiency formula.*
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Advantages and disadvantages of
different sources of energy

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Continued

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C.2. Fossil Fuels

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Origin of fossil fuels
 Fossil fuels were formed by the reduction of biological
compounds that contain carbon, hydrogen, nitrogen,
sulfur and oxygen.

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Formation of fossil fuels
• The energy from fossil fuels comes from sunlight
which was trapped by green plants millions of years
ago.
• Fossil fuels are produced by the slow and partial
decomposition of plant and animal matter that is
trapped in the absence of air.
• Oxygen is lost from the biological molecules
containing carbon, hydrogen, nitrogen, sulfur and
oxygen at a faster rate than other elements which
results in reduced biological compounds which are
often hydrocarbons.
• There are 3 types: coal, gas and crude oil(petroleum)
• Fossil fuel video

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Coal
• Coal is the most abundant fossil fuel.
• It is a combustible sedimentary rock formed from the
remains of plant life which has been subjected to
geological heat and pressure.
• Coal has gone through many stages and at each stage
the percentage of carbon increases.
• Anthracite is almost pure carbon.
• Coal usually contains between 80 and 90% carbon by
mass.

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Crude oil
• Crude oil or petroleum is one of the most important
raw materials in the world today.
• It is a complex mixture of straight and branched-
chain alkanes, cycloalkanes and aromatic compounds.
• It supplies us with the fuel we need for transport and
energy generation.
• It is a very important chemical feedstock for the
production of important organic compounds like
polymers, pharmaceuticals, dyes and solvents.
• It was formed over millions of years from the remains
of marine animals and plants trapped under layers of
rock.

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Crude oil (continued)
• In the last 50 years, crude oil has overtaken coal as the
world’s most important source of energy.
• Oil and gas are easier to extract than coal since they
can be pumped instead of mined.
• We still use 90% of the refined product as fuel.
However, as supplies decrease, this proportion will fall.
• Crude oil must be refined before it is used.

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Fractional Distillation of Crude Oil
• Crude oil (petroleum) is of no use before it is refined.
• It contains a vast mixture of hydrocarbons of varying
chain lengths.
• Long-chain hydrocarbons have stronger van der
Waal’s forces between them than do the shorter
chains, so their differing boiling points can be used to
separate the crude oil into “fractions” of various chain
lengths.
• At oil refineries the various fractions are separated by
fractional distillation.
• Note – sulfur impurities must be removed first.

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• The crude oil is heated to a temperature of about
400◦C.
• At this temperature all the different components of the
mixture are vaporized and passed up a distillation
column.
• The level at which the molecules condense depends
upon their size.
• The smaller molecules between one and four carbons
collect at the top as the refinery gas fraction.
• Molecules of successively longer chains condense at
lower levels corresponding to their higher boiling points.
• Finally, there is a residue at the bottom with higher BP
under normal atmospheric conditions.

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Fractions of crude oil

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 Uses of various fractions

The fraction between 5 and 10 carbons is the most in demand (used in cars).
As a liquid, it is convenient to handle and deliver and has a relatively low bp so
it is easy to vaporize, which assists combustion.

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Cracking
• The demand for the different fractions does not
necessarily match the amounts present in the crude
oil supplied so the hydrocarbon molecules in the
crude oil need to be chemically changed.
• Hydrocarbons with up to 12 carbon atoms are in the
most demand because they are easily vaporized and
make the best fuels.
• The supply of these can be increased by breaking
down or cracking the larger molecules.
• Thermal cracking involves heating the starting
materials to high temperature. Usually straight-chain
hydrocarbons are produced.

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Catalytic cracking
• When a catalyst is used, it is called catalytic cracking.
• This allows the reaction to occur at a lower
temperature of around 500 degrees Celsius.
• It also helps give the required product by controlling
the mechanism.
• The reactions are generally complicated but do
involve carbocations which are produced and
rearranged on the catalytic surface.
• The lower temperature requires less energy and
reduces the cost of the process.

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Catalytic cracking (continued)
• The catalysts involved are:
• Alumina and silica and zeolites(minerals of Al, Si, and
Oxygen)
• Some carbon is formed during the process which can
coat the catalyst and stop it from working (poisoning)
• The catalyst must be separated from the mixture and
then the carbon is removed by heating.
• The heat produced from the combustion of the
carbon can be used to sustain the cracking reaction.
• Catalytic cracking tends to form branched chain
alkanes and benzene ring aromatics which burn more
evenly in a car engine.

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Hydrocracking
• Hydrocracking also produces compounds used in high
quality gasoline.
• In this process a heavy hydrocarbon fraction is mixed
with hydrogen at a pressure of 80 atm and cracked
over palladium on a zeolite surface.
• A high yield of branched-chain alkanes, cycloalkanes
and some aromatic compounds is produced.

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Knocking
• The fuel-air mixture in a car engine is compressed
and ignited with a spark plug.
• Some fuels auto-ignite without the need of a spark
plug.
• This premature ignition is known as “knocking” as it
gives rise to knocking sound in the engine.
• Knocking reduces engine efficiency because the
exploding and expanding gas is not applied fully to the
piston at the optimum time and can cause engine
damage.
• Straight chain molecules have a tendency to knock.

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Octane Number
• The branched-chain isomer of octane, 2,2,4-
trimethylpentane (isooctane) does not suffer from
premature ignition and is considered the standard
from which other fuels are judged.
• The performance of a fuel is given by its octane
number which is based on a scale where isooctane has
a value of 100 and heptane has a value of 0.
• A fuel with a 96% octane rating burns as efficiently as
a mixture of 96% isooctane and 4% heptane.
• Fuels with high octane numbers can be more highly
compressed, which results in more power per piston
stroke.

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Octane number (continued)
• Octane number decreases with an increase in chain
length.
• Cyclic compounds have higher octane numbers than
linear structures.
• Alkenes have a higher octane number than the
isomeric cycloalkanes.
• Aromatic compounds with the benzene ring have
even higher octane numbers.

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Catalytic reforming
• Catalytic reforming involves the rearrangement of the
atoms in a molecule to form a more branched chain
or aromatic compound.
• The process is referred to as “plat forming” if
platinum is used as the catalyst.
• Palladium, iridium and rhenium can also be used.
• Isomerization can increase the branching in a
molecule by heating them in the presence of a
catalyst such as AlCl3.
• Alkylation involves reacting lower mass alkenes with
alkanes to form higher mass alkanes.

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Alkylation
• This can be thought of as the reverse of cracking.
• It is a process in which larger alkanes are formed from
smaller molecules. This is done by adding an alkane
unit across the double bond in the alkene making a
larger branched chain alkane.These reactions are
catalyzed by alkylating agents

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Alkylation (continued)

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Coal liquefaction
• Reacting coal with hydrogen under high
pressure in the presence of a catalyst
produces liquid hydrocarbon fuels.
• The resulting mixture can be separated by
fractional distillation.
• As crude oil prices rise, this will be an
increasingly economic option.
• The formula for this process is:
 nC + (n+1)H2 → CnH2n+2
 where n>4

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FISCHER-TROPSCH PROCESS
• This process involves using a mixture of
carbon monoxide and hydrogen as the
feedstock and produces a variety of alkanes
along with water.

• The formula for this process is:

 (2n+1)H2 + nCO → CnH2n+2 + nH2O

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Natural Gas
• Natural gas is the cleanest of the fossil fuels to burn
due to its high hydrogen to carbon ratio.
• Impurities can easily be removed so the combustion
of natural gas produces minimal amounts of carbon
monoxide, hydrocarbons and particulates.
• Where it is available, it takes little energy to get from
ground to the consumer since it can be piped directly.
• However, setting up a distribution network requires a
massive capital investment.
• Some countries use liquefied gas (butane or propane)
as an option for domestic heating and cooking.

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Natural Gas (continued?
• Methane is the primary component of natural gas.
• Natural gas was formed millions of years ago by the
action of heat and pressure and bacteria on buried
organic matter.
• The gas is trapped in geological formations capped by
impermeable rock.
• It is also formed from the decomposition of crude oil
and coal deposits.
• It can occur on its own, dissolved under pressure in oil,
or in a layer above oil in a reservoir.
• Natural gas can also be found with coal, where it is a
major hazard as it forms an explosive mixture with
air.
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COAL GASIFICATION
• Coal can be converted to methane by the process of
coal gasification.
• The crushed coal is mixed with superheated steam
and a mixture of carbon monoxide and hydrogen
known as synthesis gas is produced.
C(s) + H2O(g) → CO(g) + H2(g)
• Synthesis gas can be used directly for fuel or
processed further to make methane.
 CO(g) + 3H2(g) → CH4(g) + H2O(g)

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Synthetic Natural Gas
• Synthetic natural gas can also be made by
heating crushed coal in the presence of steam
with a potassium hydroxide catalyst to
produce methane and carbon dioxide.
2C(s) + 2H2O(g) → CH4(g) + CO2(g)

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Carbon Footprint
• One measure of the impact our activities have on the
environment is given by our carbon footprint.
• The carbon footprint is a measurement of all the
greenhouse gases (primarily CO2 and CH4) we
individually produce.
• It has units of mass of carbon dioxide (sometimes
expressed as equivalent tons) and depends on the
amount of greenhouse gases we produce in our day-
to-day activities through the use of fossil fuels such as
heating, transport and electricity.

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Example
• Work out the carbon footprint for a car journey of 100km.
Assume that the car uses 7dm3 of fuel for the journey and
that the fuel is octane.The density of octane is .703 g/cm3.

• First determine the mass of octane burned by using the

density.
• 7dm3 x 1000cm3/dm3 = 7000cm3 x .703 g/cm3 = 4921 g
• Convert from grams to moles by dividing by the molar
mass of octane.
• 4921 g x mol/114.3 g = 43.07 mol
• Solve for moles of CO2 produced. 43.07mol x 8/1 = 345
mol CO2
• Solve for grams of CO2. 345 mol x 44.01g/mol = 15200 g or
15.2 kg
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Example 2
• On a typical winter day 1.33 x 106 kJ of energy is needed in
a home.

• A) Calculate the percentage mass of carbon in the two

fuels.
• B) Determine the carbon footprint of the two fuels.

• Coal is CH. % C is 12.01/13.02 x 100 = 92.2 %

• Wood is C5H9O4. % C is (5 x 12.01)/(5x12.01 + 9x1.01 +
4x16) x 100 = 45.1%

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Continued
 B) Determining the carbon footprint of the two fuels.
 Coal: efficiency = useful output energy x 100 = 65%
 total input energy
 Solve for input energy needed: input = 1.33x106kJ/.65 = 2.05X106 kJ
 Use specific energy to solve for mass of fuel: 2.05X106kJ x g/31kJ = 66000 g
 Use % carbon to solve for mass of carbon burned: .922(66000g)=60800gC
 Solve for mass of CO2: 60800gC x 44.01gCO2/12.01gC=22300g = 223kg CO2

 Wood: efficiency = useful output energy x 100 = 70%

 total input energy
 Solve for input energy needed: input = 1.33x106 kJ/.70 = 1.9X106 kJ
 Use specific energy to solve for mass of fuel. 1.9X106kJ x g/22kJ = 86400 g
 Use % carbon to solve for mass of carbon burned: .451(86400g)=38900gC
 Solve for mass of CO2: 38900gC x 44.01gCO2/12.01gC=14200g = 142kg CO2

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Example 3

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ADVANTAGES AND DISADVANTAGES
OF FOSSIL FUELS
COAL
• ADVANTAGES
• Cheap and plentiful throughout the world
• Can be converted to synthetic liquid fuels and gases.
• Safer than nuclear power
• Ash produced can be used in making roads.

• DISADVANTAGES
• Produces many pollutants including CO2 and SO2 and
particulates
• Difficult to transport
• Waste can lead to visual and chemical pollution
• Mining is dangerous.
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CRUDE OIL
• ADVANTAGES
• Easily transported in pipelines or by tankers.
• Convenient fuel for cars as it is volatile and burns easily.
• Sulfur impurities can easily be removed.

• DISADVANTAGES
• Limited lifespan and uneven world distribution.
• Contributes to acid rain and global warming.
• Transport can lead to pollution.
• CO is a local pollutant produced by incomplete
combustion of gasoline.
• Photochemical smog is also produced.

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Natural Gas
• ADVANTAGES
• Produces fewer pollutants per unit energy.
• Easily transported in pipelines and pressurized containers.
• Does not contribute to acid rain.
• Higher specific energy.

• DISADVANTAGES
• Limited supplies.
• Contributes to global warming.
• Risk of explosion due to leaks.

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Summary

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Impact of fossil fuels on the
environment
• NOTE – ALL FOSSIL FUELS ARE NON-
RENEWABLE AND PRODUCE THE GREENHOUSE
GAS CARBON DIOXIDE.
• The choice of fossil fuels used by different
countries depends upon historical, geological and
technological factors. Different societies have
different priorities in their energy choices.
• As civilization has advanced, the carbon content
of fossil fuels has decreased.
• Coal has been replaced by gasoline and natural gas because they
have higher specific energies and energy densities and are easier
to transport.They are also cleaner burning and produce less CO2
per unit energy.

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Continued
• The financial costs involved in constructing
international pipelines is a main reason why the
international trade in natural gas has been relatively
slow.
• At present most natural gas is consumed in the
countries in which it is found.

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Next C.3.Nuclear Energy

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