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Chapter 9. Energy Sources. Section 1. Fossil Fuels. Using Energy. Thermal, electrical, mechanical energy – ALL the time Use means transform energy from one form to another Useful and non-useful transformations. Use in the US. We use more energy than anyone else in the world.

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Chapter 9 l.jpg

Chapter 9

Energy Sources

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Section 1

Fossil Fuels

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Using Energy

  • Thermal, electrical, mechanical energy – ALL the time

  • Use means transform energyfrom one form to another

  • Useful and non-useful transformations

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Use in the US

  • We use more energy than anyone else in the world

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Making Fossil Fuels

  • Fossil Fuels – petroleum, oil, coal, and natural gas formed from decaying ancient plants and animals over millions of years

  • Combustion reactions take chemical potential energy  heat and light

  • Fossil Fuels – energy is concentrated

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  • Def: (crude oil) highly flammable liquid formed by decayed ancient organisms

  • Hydrocarbon – contain only hydrogen and carbon

  • Contains many dif. Hydrocarbons

  • Separate by Fractional Distillation – tall towers of refineries

  • Heat and dif. hydrocarbons have dif. boiling points

  • Lowest bp on top – highest on bottom (liquid asphalt)

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Petroleum Uses

  • Plastics and synthetic fabrics

  • Grease, Vaseline, motor oil

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Natural Gas

  • Rise to top of petroleum deposits in ground

  • Contains Methane CH4, Propane C3H8 and Butane C4H10

  • Makes up ¼ of energy consumed in US

  • More energy than petr. and burns cleaner

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  • Until 1950s almost half energy in US was from coal

  • Today it is ¼ and 90% is used to make electricity in power plants

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Origin of Coal

  • Coal mines were once swamps

  • Estimated 20 – 40 times more coal than petroleum

  • Coal not as pure as other Fossil Fuels – has more sulfur and nitrogen

  • Leads to more pollutants

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Generating Electricity

  • Burn fuel – thermal energy – heat water – steam – spins turbine – spins magnet in generator – electricity!

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Cost of Using Fossil Fuels

  • Burning Coal and Petroleum give off particulates – can cause breathing problems

  • CO2 given off = global warming

  • Coal – very dirty – sulfur pollutants = acid rain

  • Mining is very dangerous

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Nonrenewable Resources

  • Def: cannot be replaced as quickly as being used

  • Increase cost = more difficult to get

  • Push for “renewable” sources to help energy demand

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Chapter 9 Section 2

Nuclear Energy

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Using Nuclear Energy

  • No Fossil Fuels

  • Nuclear energy (energy released when nucleus breaks apart – nuclear fission)  electrical energy

  • 20% of electricity produced in US

  • In 2003 – 104 nuclear reactors in 65 nuclear power plants in US

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Nuclear Reactors

  • Def: uses energy from controlled nuclear reactions to generate electricity

  • Fuel – undergoes fission

  • Control rods – control reaction

  • Cooling system

  • Core is very small part

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Nuclear Fuel

  • Only certain elements can undergo fission

  • Uranium, U-235

  • Fuel normally uranium dioxide

  • Use enriched Uranium so its 3-5% U-235

  • Fuel is in tiny pellets

  • Core has 100,000 kg of uranium

  • In 100s of fuel rods

  • 1 kg U undergoes fission =

  • Energy of 3 million kg of coal

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Nuclear Fission

  • A nuclear chain reaction happens in milliseconds

  • # nuclei at each stage doubles  after 50 stages a quadrillion nuclei may split

  • If not controlled, will release energy explosively

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Controlling Reactions

  • Control rods absorb some neutrons

  • Moving the rods deeper in the core  absorb more neutrons = slows reaction

  • Eventually energy is released at a constant rate

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Nuclear Power Plants

  • Energy released by fission = thermal energy – heats steam, etc.

  • Efficiency is 35%

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The Risks!

  • Good = no fossil fuels, no pollutants

  • Bad:

  • Mining of U has environmental problems

  • Water used needs to cool before released in streams

  • Escape of harmful radiation – have elaborate safety systems

  • p. 268

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Disposal of Waste

  • After 3 years U-235 is spent = Nuclear Waste – radioactive by products

  • Low-level wastes – clothing exposed to radiation, air filters or smoke detectors

    • Buried in sealed containers 30 m deep

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Disposal Tanks

  • High-level wastes – power plants and weapons

    • Stored in deep pool of water

    • Sealed in ceramic glass in metal-alloy containers buried 100s of meters – won’t contaminate for 1000s of years

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Chapter 9 Section 3

Renewable Energy Sources

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Renewable Resources

  • Def: Energy source replaced nearly as quickly as used

  • Energy from Sun:

  • Amt of solar energy falls on US in a day is more than energy used in 1 year

  • Photovoltaic Cell: (solar cell) take radiant solar energy  electrical energy

  • 7-11% efficient

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How Solar Cells Work

  • Sunlight hits e-rich semiconductor  e-poor semiconductor = electric current sent through metal

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Using Solar Energy

  • Solar electricity is more expensive but in remote areas it is good

  • Best way is a parabolic trough – focuses sunlight on tube – synthetic oil or liquid salt

  • Heat liquid  heats water = steam to spin generator

  • Plant in the Mojave Desert = 9 units, 350 megawatts – 500,000 people

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Energy from Water

  • Hydroelectricity: electricity produced from energy of moving water

  • Produces 8% of electricity used

  • Twice as efficient because of no heat and no pollutants

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Energy from Water

  • Problems:

  • Artificial dams damage natural ecosystem

  • Water reservoirs aren’t everywhere

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Energy from Tides

  • Rising tide comes in – spins turbines and is trapped

  • Decreasing tide flows back out – spins turbines

  • Need to have tide dif of 5 m

  • 1 in North America – Annapolis Royal, Nova Scotia – tide dif 17 m

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Harnessing the Wind

  • Wind spins propeller – connected to generator

  • Few places have constant wind

  • 20% efficient

  • Noisy – change appearance of landscape

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Energy from Inside Earth

  • Decay of radioactive elements = geothermal heat  makes magma

  • Geothermal Energy: thermal energy in hot magma

  • Old Faithful – water heated by magma close to surface

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Energy from Inside Earth

  • Water pumped in ground – heated – steam released

  • 16% efficient

  • Can release sulfur compounds

  • Limited to areas where magma is close to surface

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Alternative Fuels

  • Hybrid vehicles – use electric batteries and gasoline

  • Hydrogen gas – produces only water vapor when burned

  • Biomass Fuels: renewable organic matter, wood, sugarcane fibers, rice hulls, and manure

  • Burned in oxygen to convert chemical energy  thermal energy  heat water, etc.