Energy and the Environment Science 30: Unit D Chapter 1: Limitless energy.
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Transcript of Energy and the Environment Science 30: Unit D Chapter 1: Limitless energy.
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Energy and the Environment
Science 30: Unit DChapter 1: Limitless energy
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1.1- Energy on Demand
• Energy is not a limitless resource; Canadians are not making energy-conscious decisions.• From 1990-2002 a shift towards SUV’s increased fuel
consumption by $370/year compared to cars.• GDP (gross domestic product) is $753 billion; leads to
increase energy use to manufacture goods.• Energy intensity is calculated by dividing energy use
by GDP per year; industrialized countries have low values.
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1) Factors affecting usage
Climate: extremes in temperature influence energy usage.• Canada = used to heat homes• Australia= used to cool homes• Changes cause huge variance (47.9 PJ)
Activity: how much work is being done• Measured in $, tones, km travelled.• AS GDP increases; activity increases;
energy usage increases.
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Factors affecting usage
• Population: energy use per capita.• Used to measure prosperity of a country.• In order to become prosperous, energy
use is increased= consequences for environment.
• Energy intensity: energy used/ GDP.• Natural resources industry requires more
energy usage = higher intensity.• Since 1990’s Canada has developed a less
energy-intensive economy
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2) Energy Efficiency
• Energy transformation is NOT 100%; some is lost as waste energy.
• The desired energy is “useful” energy; the total energy used is the “input” energy.
• To calculate efficiency:• Efficiency = energy (or work) output
energy (or work) input
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A) Kinetic and Potential energy example
2. A person on a rollercoaster starts with 345J of Potential energy; the energy at the end of the rollercoaster is 120J of Kinetic energy. What is the efficiency of the rollercoaster?
% efficiency = output energy/input energy
= Kinetic energy/Potential energy
= (120J/345J) x 100
= 34.78%
b) What percent of the total energy is lost as waste energy (heat, sound, etc.)?
100% - efficiency = waste energy %
100% - 34.78% = 65.22%
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B) Percentage example3. If a machine is 52% efficient and the total
energy output is 235J; what is the energy input?
% efficiency = energy output/energy input
Energy input = energy output / % efficiency
= 235J/0.52
= 452J
b) What is the energy (in Joules) that is lost to the surroundings?
100% - % efficiency = 48%
0.48 x 452J = 217J
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c) Efficiency improvements
• Replacing incandescent light bulbs with fluorescent saves energy.
• From 1990-2002 the energy use in mining decreased by 12% but the amount mined did not.
• Royalties are paid to Alberta’s government by energy companies in order to offset the environmental cost.• Recall Stelmach and the royalty scandal last
year?Gas and Oil
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1.3) Harvesting Chemical Energy
• Fossil fuels are used to power engines as well as electronics; where and how they are made is important.
• Discarding rechargeable batteries can lead to soil contamination from heavy metals.
• Energy released in combustion reactions (from fossil fuels) releases carbon dioxide and water vapor.• Chemical potential energy
changes.• Hydrocarbons contain lots of
energy
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1) Energy release
• Energy from combustion reactions takes many forms:• Radiant energy (IR and visible light).• Kinetic energy (movement increases)
• Products are at a higher temperature; transfer of energy from hot to cold is called “heat”.
• Energy released is useful “movement” or waste “heat”.
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2) Heat of combustion• Reactants have more
chemical energy – products have more kinetic.
• Potential energy changes in combustion reactions; products have less stored energy than reactants.• Difference = energy released.
• Heat of combustion( ∆cH°) is the energy released during the exothermic (energy released) reaction.
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a) Calorimetry
• A calorimeter is used to measure energy transferred to water from the substance being burned.
• An experimental value for heat of combustion is given, but there are errors due to waste energy lost.
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b) Hess’s Law
ΔcH° = ∑ΔfH°products – ∑ΔfH°reactants
• Uses standard heat of formation (energy it takes to form a compound) to estimate potential energy.
• Standard heat of formation ( ∆fH°):
• element = 0 kJ• Substances = value from chart (p.5)
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Steps
1. Divide into products and reactants.
2. Identify # moles for each
3. Assign values from page 5 table.
4. Total and subtract from each other.
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Hess’s law examples
• Calculate the energy change in combustion for the following (use the table):
CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (l)
C4H10 (g) + 13 O2 (g) → 8CO2 (g) + 10 H2O (l)
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3) Inefficiency of machines
Total energy input = total energy transferred out (First law of thermodynamics).
Some energy will always pass to the environment as heat = 2nd law (always from hot to cold object).
Minimizing the heat loss is the important challenge.
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4) Coal-fired generators
• Coal is used to produce more than 70% of Alberta’s electricity.• Converts chemical potential energy into
electrical energy.
• Process:• Crush coal to fine dust, blow into combustion
chamber, IGNITE.• Energy released is absorbed by water lining
the chamber.• Water is converted to steam; causes turbine to
spin--- connected to generator.
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Energy conversion:
1. Chemical potential
2. Kinetic energy (steam)
3. Kinetic energy (turbine)
4. Kinetic energy (generator)
5. Kinetic energy (electrical lines)
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1.4) Harvesting Nuclear energy
• CANDU = nuclear reactor developed in Canada (Canadian Deuterium Uranium reactor).
• Nuclear energy results from the nucleus of atoms; combining 2 particles or splitting them.
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1) The nucleus
• There are 3 subatomic particles in the nucleus:• Proton = positive charge, mass of nucleus,
atomic number.• Neutrons = no charge, mass of nucleus,
responsible for isotopes ( different numbers of neutrons, same protons).
• Electrons = negative charge, orbit nucleus, responsible for charge.
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a) Nucleons
Protons and neutrons compose nucleus = nucleons.
Use nuclear notation to describe nucleons:
Mass # - Atomic # = neutrons.
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b) Stable Vs Unstable Nuclei
• Stable nucleus = one that will stay together indefinitely
• What makes a nucleus stable?
• Strong Nuclear Force which is much stronger than the electric repulsive forces pushing protons apart.
• Strong nuclear forces only work over very short distances.
• In a large nucleus or a nucleus with extra neutrons, Strong Nuclear Forces don’t work as well and the nucleus is unstable.
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2) NUCLEAR REACTIONS
• Chemical reactions, like combustion, only involve changes to electrons.
• NUCLEAR reactions involve changes within the nucleus – new elements are sometimes formed as a result.
• 3 Types of NUCLEAR REACTIONS:• Radioactive decay• Nuclear fission• Nuclear fusion
Nuclear Notation
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a) Radioactive decay
• If the force in the nucleus is unstable, the neutron responsible will force the nucleus to split.
• The split nucleus = 2 alpha particles.
• Alpha particle = 2 p+ and 2n (charge = 2+); often written as a helium atom.
• Release of alpha particles = alpha radiation; usually only 1 product is an alpha particle.
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Radioactive decay: Types of Radiation
• ALPHA radiation is a particle consisting of two protons and two neutrons (helium nucleus)
• BETA Radiation is high speed electrons produced by changing one neutron into a proton and an electron.
• GAMMA radiation are high energy photons.
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1) Alpha decay
Number of radioactive nucleons must balance between reactants and products.
1 product is always an alpha particle ( 4 nucleons, 2 protons).
alpha decay process
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steps1. Split reaction into
reactants and products (1 product is always an alpha particle).
2. Create a table.
3. Calculate the mass # and Atomic # of unknown.
4. Identify which element it is (by atomic #).
5. Write the balanced reaction.
reactant product
Mass # 6 4 + AAtomic # 3 2 + Z
63Li ---> 4
2He + ?
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2) Beta Decay
• Instability in the nucleus leads to a beta particle (an electron) emission.
• Emitted from the nucleus; a stream of beta particles = beta radiation.
• In beta decay, # of nucleons is constant but atomic # changes; causes conversion of 1 neutron into a proton.
beta decay process
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steps1. List reactants and
products.
2. Create a table:
3. Determine mass # and atomic # of the product.
4. Identify unknown product (Atomic # = protons).
5. Write balanced equation.
reactant product
Mass # 10 0 + A
Atomic # 4 -1 + Z
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3) Gamma Radiation
• Composed of photons with no mass or charge:
• Usually an excess product of alpha and beta decay.
• Are harmful to humans; considered to be ionizing radiation.
Radioactive Decay
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Shielding radiation
• Alpha, Beta and Gamma rays are ionizing radiation and must be shielded.
• A Geiger counter is used to test how much radiation escapes the container (shield).
• Shielding is most difficult for gamma rays because they are the smallest; then beta and finally alpha.
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Energy of Different Types of Radiation
• Each type of radiation has a different amount of energy as shown by the penetrating power.
• Alpha is stopped by paper
• Beta is stopped by a thin sheet of copper or a wood or a flesh
• gamma is only stopped by a thick sheet of lead.
Radioactivity
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b) Nuclear Fission
• Energy is created by splitting an atom; a large nucleus is struck by a neutron and breaks into 2 smaller nuclei.
• Used in the 1st atomic bomb; used to generate electricity (CANDU reactor).
• Products of the reaction have high kinetic energy; used to spin generators = electricity.
Nuclear Fission
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1) Balancing equations
• Same as the steps to balance all other types of radiation.
• Complete the following:235
92U+ 10n ---> 3 1
0n + AZX + 137
53I
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2) Controlling the Fission reaction
1) CANDU reactor controls neutrons available by using heavy water = uses heavy hydrogen and oxygen.• Controls the speed of the neutrons.• AKA = moderator (moderates speed).
2) Control rods = lower into Uranium core, decreasing fission reaction #’s.
• Prevents the uncontrolled chain reaction = nuclear meltdown.
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Chernobyl Nuclear Meltdown
Chernobyl videos
Chernobyl remembered - MSN Video
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3) Mass-Energy Equivalence
• An uranium pellet of 7g can release same amount of energy as 560 L of oil.
• Einstein explained that mass and energy can be converted.
• Mass is the sum of all energy; energy is conserved not mass.
• Uses equation:
E = mc2Energy-mass
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a) Energy problems
• A small change in mass can create a huge change in energy.
• Sun converts 4.2 x109 kg into energy per second.
• Balance nuclear equations as usual but find masses from the data booklet.
• Find mass for reactants, products and change in mass.
• Calculate the energy given off.See page 515 problem 1.8
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3) Nuclear Fusion• energy of stars
• 2 small masses combine to form larger masses
• Extremely high temperatures required, so fusion reactions are called thermonuclear
• sun temperatures are ~ 15 000 000 ºC
• Fusion bomb = H bomb - fission reactions are used to create high enough temps to have a fusion reaction happen.
• Slow controlled release of energy from a fusion reaction escapes physicists.• Has been pursued for over 40 years• Scientists claimed they had a cold fusion reaction but it
has not ever been proven or replicated.• Ongoing research• Enormous potential energy and the fuel for this type of
reaction is almost unlimited.
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Fusion video