air, earth, fire and water an introduction to environmental science energy ~ fossil fuels
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TRANSCRIPT
Unit 1 ~ Energy ~ Fossil Fuels 2
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
Unit 1 ~ Energy ~ Fossil Fuels 3
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.
Unit 1 ~ Energy ~ Fossil Fuels 5
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.
Unit 1 ~ Energy ~ Fossil Fuels 6
Types of Fossil Fuels
• Coal
• Oil
• Gas
• Peat
Unit 1 ~ Energy ~ Fossil Fuels 7
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.
Unit 1 ~ Energy ~ Fossil Fuels 8
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.
Unit 1 ~ Energy ~ Fossil Fuels 9
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)
Unit 1 ~ Energy ~ Fossil Fuels 10
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
Unit 1 ~ Energy ~ Fossil Fuels 11
Burning natural gas
http://www.marymount.k12.ny.us/marynet/stwbwk05/05flashchem/lyreaction/lyreaction.html
Unit 1 ~ Energy ~ Fossil Fuels 12
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
Unit 1 ~ Energy ~ Fossil Fuels 13
The calculationHeat 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)
Unit 1 ~ Energy ~ Fossil Fuels 14
Different Types of Fuels ~
Solid, Liquids, Gases • Predict what types of fuel you think would
give the most energy?
• Why?
Ethanol
Gas
Kerosene Coal
Oil
Unit 1 ~ Energy ~ Fossil Fuels 16
Exothermic and Endothermic Reactions
http://www.bbc.co.uk/schools/gcsebitesize/chemistry/chemicalreactions/2energychangesrev2.shtml
Unit 1 ~ Energy ~ Fossil Fuels 17
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)
Unit 1 ~ Energy ~ Fossil Fuels 21
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.
Unit 1 ~ Energy ~ Fossil Fuels 22
Energy Loss
Common Areas of Energy Loss:• Radiation• Conduction• Convection• Condensation• Air Infiltration• Leaving Electrical Items on Standby• Energy Efficient Light Bulbs
Unit 1 ~ Energy ~ Fossil Fuels 24
Energy Types
Types of Energy:• Nuclear• Kinetic• Potential• Heat • Sound• Light• Electrical
Unit 1 ~ Energy ~ Fossil Fuels 26
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.