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376328113-c-1-Energy-Sources

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OPTION C: ENERGY
C.1
ENERGY SOURCES
By: Merinda Sautel
Alameda Int’l Jr/Sr High School
Lakewood, CO
msautel@jeffco.k12.co.us
ESSENTIAL IDEA
Societies are completely dependent on
energy resources. The quantity of energy is
conserved in any conversion but the quality
is degraded.
NATURE OF SCIENCE (2.2)
Use theories to explain natural phenomena—energy
changes in the world around us result from potential
and kinetic energy changes at the molecular level.
Energy has both quantity and quality.
INTERNATIONAL-MINDEDNESS
The International Energy Agency is an
autonomous organization based in Paris which
works to ensure reliable, affordable and clean
energy for its 28 member countries and beyond.
The International Renewable Energy Agency
(IRENA), based in Abu Dhabi, UAE, was
founded in 2009 to promote increased adoption
and sustainable use of renewable energy sources
(bioenergy, geothermal energy, hydropower,
ocean, solar and wind energy).
THEORY OF KNOWLEDGE
“I have no doubt that we will be successful in
harnessing the sun’s energy. If sunbeams were
weapons of war we would have had solar energy
centuries ago.” (Lord George Porter). In what ways
might social, political, cultural and religious factors
affect the types of research that are financed and
undertaken, or rejected?
There are many ethical issues raised by energy
generation and its consequent contributions to
pollution and climate change. What is the influence
of political pressure on different areas of
knowledge?
UNDERSTANDING/KEY IDEA
C.1.A
A useful energy source releases energy
at a reasonable rate and produces
minimal pollution.
USEFUL 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 problem is that the “quality” of our energy is
being degraded.
If we lose energy to the environment, it is no longer
available to do useful work.
USEFUL ENERGY
• 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.
UNDERSTANDING/KEY IDEA
C.1.B
The quality of energy is degraded as heat
is transferred to the surroundings.
Energy and materials go from a
concentrated into a dispersed form. The
quantity of the energy available for doing
work decreases.
UNDERSTANDING/KEY IDEA
C.1.C
Renewable energy sources are naturally
replenished.
Non-renewable energy sources are
finite.
APPLICATION/SKILLS
Be able to discuss the use of different
sources of renewable and
non-renewable energy.
RENEWABLE VS
NON-RENEWABLE
• 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.
Coal – millions of years for fossil fuels to form
UNDERSTANDING/KEY IDEA
C.1.D
Energy density=energy released from fuel
volume of fuel consumed
UNDERSTANDING/KEY IDEA
C.1.E
Specific energy=energy released from fuel
mass of fuel consumed
ENERGY DENSITY
SPECIFIC ENERGY
• Specific factors need to be taken into
consideration for storage and transport of a fuel.
Energy density – energy produced per unit volume
Specific energy – energy produced per unit mass
• These are inter-related via the density of the fuel.
• Specific energies and energy densities are never
negative values.
APPLICATION/SKILLS
Be able to determine the energy
density and specific energy of a fuel
from the enthalpies of combustion,
densities and the molar mass of fuel.
EXAMPLE 1
The enthalpies of combustion of a range of organic
compounds are given in section 13 of the IB Data Booklet.
Calculate the specific energy and energy density of hexane
from its density which is 0.6548 g/cm 3 under standard
conditions.
What info do you need?
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
EXAMPLE 1 - WORKED
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/cm 3.
What do we need? Specific energy=energy released
mass of fuel
Make the UNITS work out in thermo problems. From the
formula above we need kJ/g. How do we get these units
from the given information?
EXAMPLE 1 - WORKED
If we divide the enthalpy of combustion by the molar mass,
we will have the correct units.
-4163 kJ x mol = 48.3 kJ/g which is specific energy
mol 86.2g
Now we need - Energy density =energy released
vol of fuel
From this formula, we need kJ/cm 3 so multiply the specific
energy by the density.
48.3kJ x 0.6548 g = 31.6 kJ/cm3 which is energy density
g
cm3
EXAMPLE 2
The standard enthalpy of combustion of carbon is -394
kJ/mol. The density of anthracite, one of the purest coals, is
2267 kg/m3. Use this information to calculate the energy
density and specific energy of this form of coal.
Specific energy = 32.8 kJ/g
Energy density = 7.44 x 10 7 kJ/m3
EXAMPLE 3
Ethanol is a fuel produced from plant products by
fermentation. It has a density of 789 g/dm 3 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” chemistry even
though it produces CO 2 in the combustion reaction.
EXAMPLE 4
The enthalpies of combustion of methane and hydrogen are
given in section 13 of the IB data booklet.
a). Calculate the specific energies of CH 4 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.
APPLICATION/SKILLS
Be able to discuss how the choice of
fuel is influenced by its energy density
or 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.
UNDERSTANDING/KEY IDEA
C.1.F
The efficiency of an energy transfer =
useful output energy x 100
total input energy
ENERGY EFFICIENCY
• A primary source of energy is often not used but
converted to a secondary source such as
electricity and some energy is lost in this
conversion.
• No matter how well a power plant is designed it
can never convert energy from one form to
another with 100% efficiency.
• The efficiency is usually less than 50%.
APPLICATION/SKILLS
Be able to determine the efficiency of
an energy transfer process from
appropriate data.
EXAMPLE 5
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.
EXAMPLE 5 WORKED
You need the formula: efficiency = useful output energy x 100
total input energy
What are the givens?
Efficiency = 36% and rate = 5.50 x 10 8 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
EXAMPLE 5 WORKED
b) efficiency = useful output energy x 100 = 36%
total input energy
useful output energy = .36
total input energy
You just calculated output energy in “a”.
Rearrange the equation so input energy = output/.36
Input energy = 1.73 x 10 16 J/.36 = 4.82 x 10 16 J
EXAMPLE 5 WORKED
c) Heat energy = 4.82 x 1016 J = 4.82 x 1013 kJ
To solve for moles, use the enthalpy of combustion.
4.82 x 1013 kJ x mol = 1.22 x 1011 mol
394kJ
To solve for mass, multiply by the molar mass.
1.22 x 1011 mol x 12.01 g/mol = 1.47 x 1012 g
EXAMPLE 6
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 gasburning power plant (efficiency 50%). Determine the mass of
methane needed to generate the electricity needed to heat the
house.
*Please note that the input energy must be larger than the output
energy. Use this rule of thumb when using the efficiency formula.*
APPLICATION/SKILLS
Be able to discuss the advantages and
disadvantages of the different energy
sources in C.2 through to C.8.
CITATIONS
International Baccalaureate Organization. Chemistry Guide,
First assessment 2016. Updated 2015.
Brown, Catrin, and Mike Ford. Higher Level Chemistry. 2nd
ed. N.p.: Pearson Baccalaureate, 2014. Print.
ISBN 978 1 447 95975 5
eBook 978 1 447 95976 2
Most of the information found in this power point comes
directly from this textbook.
The power point has been made to directly complement the
Higher Level Chemistry textbook by Brown and Ford and is
used for direct instructional purposes only.
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