Air, Earth, Fire and Water
An Introduction to Environmental
Science
Energy ~ Fossil Fuels
Energy ~ Some Basic Ideas
• Energy is the ability to do work
• It is measured in J or kJ
• Energy can be converted from
one form to another
• There are many different types
of energy: Kinetic, Potential,
Nuclear, Chemical, Electrical,
Magnetic, Heat, Sound
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Formation of Fossil Fuels
• Work is the transfer of energy.
• About 300 million years ago huge forests
covered many areas.
• These forests died and were replaced by others;
until over the ages a thick layer of plant matter
was built up this was called peat.
• Over the years the seas came in and covered
the peat with mud and sand. Thousands of years
later the seas retreated and new forests grew.
This happened many times and the compressed
peat turned into coal.
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Formation of coal
www.minepermits.ky.gov/.../coal_formation.htm
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Formation of Fossil Fuels
• As this vegetation decays, the peat changes to
coal, and methane gas is also formed.
• Over the ages huge quantities of methane gas
have been trapped under impervious rocks.
• These methane sources have been found in
many places including the North Sea and off the
South coast of Ireland.
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Types of Fossil Fuels
•
•
•
•
Coal
Oil
Gas
Peat
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What is a Fuel
• A fuel is a substance which can be used
as an energy source.
• We can burn fuels to create energy to
power our homes, our cars and industry.
• The amount of energy a fuel contains can
be measured by burning a known mass
• This gives us the fuels heat of combustion
in kJ/kg.
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Heat of combustion
• Heat of combustion of a substance is the
heat change which occurs when one mole
of the substance is burned in an excess of
oxygen.
• A reaction in which heat is liberated is
known as an exothermic reaction.
• A reaction in which heat is taken in is
known as an endothermic reaction.
• Combustion reactions are exothermic.
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Burning of fossil fuels
Carbon:
C (s) + O2 (g) → CO2(g)
Methane:
CH4 (g) + 2O2 (g) → CO2 (g)+ 2H2O (g)
Oil:
C6H6(l) + 7.5O2(g) → 6CO2(g) + 3H2O(g)
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Some fuels are better than others!
• The different fossil fuels give our different
amounts of heat/kg and produce different
amounts of CO2
• Thus some fossil fuels are better for the
environment:
Gas > oil > coal
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Burning natural gas
http://www.marymount.k12.ny.us/marynet/stwbwk05/05flashchem/lyreaction/
lyreaction.html
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Heat of Combustion
Calculate the heat of combustion of ethanol from the
following experimental results, taken using a bomb
calorimeter:
Mass of ethanol = 20 g
Mass of water in calorimeter = 10 kg
Initial temperature of water = 18 ˚C
Final temperature of water =32 ˚C
Specific Heat capacity of water = 4200 J/kg˚C
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The calculation
Heat gained by water ΔH =
(Temperature rise, ۫C) x (Mass of water in calorimeter, kg)
x (heat capacity of water, J/kg)
= 10 x 4200 x 14
= 588000 J = 588 kJ
Thus the combustion of 20g of ethanol liberates 588 kJ
1 mole of C2H5OH = 46g
Therefore combustion of 46g liberates
46 x 588 kJ = 1352 kJ/mol
20
Heat of combustion = -1352 kJ (exothermic reaction)
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Different Types of Fuels ~
Solid, Liquids, Gases
• Predict what types of fuel you think would
give the most energy?
• Why?
Kerosene
Coal
Ethanol
Unit 1 ~ Energy ~ Fossil Fuels
Oil
Gas
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Exothermic Reaction
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Exothermic and Endothermic
Reactions
http://www.bbc.co.uk/schools/gcsebitesize/chemistry/chemicalreactions/2energychan
gesrev2.shtml
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How much fossil fuels is used worldwide?
Source: Worldwatch Institute.
World Fossil Fuel Consumption per Source, 1950-1998
(in million of tons of equivalent oil)
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Irish energy use 1990-2005
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How much energy do we import?
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Where do we use energy?
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Energy in the Home
• Ireland imports most of her energy needs at
present.
• We are still using fossil fuels to power most of
our homes.
• By completing an energy audit on your homes
use can determine how much of these fuels you
are using unnecessarily.
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Energy Loss
Common Areas of Energy Loss:
• Radiation
• Conduction
• Convection
• Condensation
• Air Infiltration
• Leaving Electrical Items on Standby
• Energy Efficient Light Bulbs
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Energy Loss
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Energy Types
Types of Energy:
• Nuclear
• Kinetic
• Potential
• Heat
• Sound
• Light
• Electrical
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Energy Efficient Home of the Future
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Conclusion
• Energy is something that we use in
everything we do in every aspect of our
lives.
• Fossil fuels are being depleted rapidly and
cause harmful gas emissions when they
are burned to produce energy.
• We should all watch our energy
consumption in order to save energy for
the future.
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