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Explore the formation, obtaining, and usage of fossil fuels such as coal, natural gas, and petroleum. Learn about combustion reactions, fractional distillation, and the cost and environmental impact of using fossil fuels.
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Chapter 8 Energy Sources and the Environment
Section 1 – Fossil Fuels • Energy Resources • Energy is used all the time in nature • Thermal energy – furnaces, stoves • Mechanical energy – cars, vehicles
Energy Transformation • The Laws of Conservation of Energy State: • Energy cannot be created or destroyed • To use energy, energy must be transformed into another formto perform a function • Energy can be transformed to forms that are not useful • Example: Electricity flowing through power lines • 10% is lost to thermal energy
Energy Use in the United States • The US uses more energy than any other country in the world. • The US is an industrialized country • Example: graphs from 2008 show energy uses in the United States
Fossil Fuel Formation • What are fossil fuels? • Coal • Natural gas • Petroleum (Crude oil) • How are fossil fuels formed? • Formed from the dead and buried remains of once living organisms over the course of many years
Combustion Reactions • How do we use fossil fuels? • Fossil fuels contain energy in the form of chemical potential energy that is stored in fossil fuels • Fossil fuels’ stored energy is far higher than other organic substances • Example: burning 1kg of coal releases two to three times as much energy as burning 1kg of wood
Formation and Obtaining Fossil Fuels • How do fossil fuels form and how do we get them? • Because they are formed from once living organisms, fossil fuels are stored naturally underground • Fossil fuels must be mined
Petroleum • Petroleum: a highly flammable liquid formed from the decay of organisms, such as plankton and algae • Humans pump millions of liters of petroleum every day • A mixture of many different unique chemical compounds • Most are hydrocarbons • Contain hydrogen and carbon • High energy bonds • Bonds are broken when burned
Fractional Distillation • Because petroleum contains many different types of hydrocarbons, they must be separated • Uses the process of fractional distillation
Fractional Distillation • This separation occurs in distillation towers at oil-refineries. • First, petroleum is pumped into the bottom of the tower and heated. • The chemical compounds in the petroleum boil at different temperatures. • Materials with the lowest boiling points rise to the top of the tower as vapor are collected. • Hydrocarbons with high boiling points, such as asphalt and some types of waxes, remain liquid and are drained off through the bottom of the tower.
Petroleum Use • About 15 percent of the petroleum-based materials that are used in the United States are not used for fuel • In addition to fuels, plastics and synthetic fabrics are made from the hydrocarbons petroleum. • Lubricants, such as grease and motor oil, as well as the asphalt used in surfacing roads, are made from petroleum.
Natural Gas • Natural gas: a fossil fuel composed mostly of methan, CH4, but it also contains other gases hydrocarbon such as propane, C3H8, and butane, C4H10. • ¼ of energy consumed in the US comes from using natural gas • Contains more chemical potential energy per kg than petroleum or coal • The cleanest burning fossil fuel
Coal • Coal: a solid fossil fuel that is found in mines • Forms from ancient swamps • Forms as plant material is buried beneath sediments, decays, and compacts • Before the 1900’s more than 90% of homes were heated by burning coal • Today, less than 25% • Coal is often burned in power plants to generate electricity
Origin of Coal • Coal is a mixture of hydrocarbons and other chemical compounds. • Compared to petroleum and natural gas, coal contains more impurities, such as sulfur and nitrogen-based compounds. • As a result, more pollutants, including sulfur dioxide and nitrogen oxides, are produced when coal is burned.
Electricity • Graph shows the percentages of energy that comes from different sources in the US
Power Plant Efficiency • Not all the chemical potential energy in the fuel is converted to electrical energy. • No stage is 100 percent efficient. Thermal energy is released into the environment. • The overall efficiency of a fossil fuel-burning power plant is about 35 percent.
The Cost of Fossil Fuels • Using fossil fuels has some negative side effects • When petroleum products and coal are burned, smoke is given off the pollutes the atmosphere with small particles • Releases carbon dioxide • Global warming can occur as a result
The Cost of Fossil Fuels • Most abundant fossil fuel is coal • Coal contains more impurities than oil or natural gas • Burning coal can release these impurities into air that is then breathed by organisms • Coal mining can also be dangerous • Inhalation • Risk of death or injury while mining
Nonrenewable Resources • Fossil fuels are nonrenewable resources • They are not regenerated in the earth as quickly as they are used • As human population increases, production of fossil fuel based products will continue to increase, reserves of fossil fuels will decrease • Fossil fuels will become more difficult to obtain • To meet demands, some are looking for alternatives such as shale deposits
Section 2 – Nuclear Energy • Nuclear Fusion • Fusion: when atomic nuclei combine at very high temperatures • The Sun is a giant nuclear reactor • This process takes a small amount of mass and converts it into huge amounts of thermal energy • Fusion is the most concentrated energy source known • Fusion-based power plants are not practical because the reaction occurs at millions of degrees Celsius
Fission • Fission: energy released when the nucleus of an atom splits apart • Extremely small amounts of mass are converted to huge amounts of energy • 9% of US electricity is made using fission • Nuclear power plants use thermal energy to generate electricity
Nuclear Reactors • Nuclear reactor: uses the energy from controlled nuclear reaction to generate electricity • All reactors share common parts • They will contain: • Fuel for fission • Control rods • Cooling system
Nuclear Reactors • The core of a reactor is the small part where fission occurs • The core contains fuel rods and control rods • Control rods absorb neutrons from radioactive decay • Water acts as a coolant to remove heat
Nuclear Fuel • Only certain elements have nuclei that can undergo fission. • Naturally occurring uranium contains an isotope, U-235, whose nucleus can be split apart. • As a result, the fuel that is used in a nuclear reactor is usually uranium dioxide.
Fuel Rods • The core of a reactor contains about 100,000 kg of uranium in hundreds of fuel rods • Cores contain pellets of uranium dioxide • Tubes of fuel rods are bundled and covered in alloys • For every kg of uranium that undergoes fission, 1g of matter is converted to energy • 1g of matter converted to energy = energy generated by burning 3 million kg of coal
The Nuclear Chain Reaction • Uranium atoms split to release neutrons which causes other atoms to split apart. This causes a chain reaction • When an atom of Uranium-235 (U-235) is hit by a neutron it splits into two smaller nuclei • This causes two or three more neutrons to be emitted • Causes a large chain reaction
A Constant Rate • As the nuclear chain reaction occurs heat is produced • Sometimes this can occur too fast creating too much heat • In this case, cooling rods are used to absorb some of the neutrons and prevent them from striking other U-235 atoms • By raising or lowering the cooling rods, the reaction can be sped up or slowed • This can allow for a constant rate to be found
Benefits and Risks of Nuclear Power • Nuclear power is used to generate electricity in a similar way to burning fossil fuels • Nuclear power plants to do not produce the same pollutants as fossil fuels and are cleaner
Benefits and Risks of Nuclear Power • Mining uranium can cause environmental damage • They do risk a nuclear meltdown • Coolant from the core must be cooled before returned to streams or rivers
The Release of Radioactivity • One of the most serious risks of nuclear power is the release of harmful radiation from power plants. • The fuel rods contain radioactive elements with various half-lives. • Some of these elements could harm living organisms if they were released from the reactor core of a nuclear power plant
The Disposal of Nuclear Waste • Nuclear waste: any radioactive material that results when radioactive materials are used. • After about three years, not enough fissionable U-235 is left in the fuel pellets in the reactor core to sustain the chain reaction. • The spent fuel contains radioactive fission products in addition to the remaining uranium.
Low-Level Waste • Contain small amounts of radioactive material • Have short half lives • By product of electricity generation, medical research and treatments, pharmaceutical industry, and food preparation • Low-level wastes are usually buried in trenches about 30m deep in special locations • If dilute, some waste is released into air or water where it will dissipate
High-Level Waste • Generated by nuclear power plants and nuclear weapons programs • After a fuel rod is spent, it is stored in a deep pool of water • Many high-level wastes have long half-lives • High-level wastes remain radioactive for tens of thousands of years • Must be stored in extremely stable containers
High-Level Waste • One method of long-term waste storage incases radioactive wastes in glass and ceramic then placed in protective metal containers • Containers are then buried hundreds of meters below ground in stable rock formations or salt deposits
Section 3 – Renewable Energy Resources • Energy Options • Renewable Resources: an energy source that is replaced by natural processes faster than humans can consume the resource • Demand for energy increases as Earth’s population increases • Other sources must be used to meet the demand • Some alternatives are renewable
Energy From the Sun • Photovoltaic cells: convert radiant energy from the sun directly into electrical energy • About 1 billionth of the suns energy strikes earth • The suns energy should last for billions of years – it’s inexhaustible • Solar energy is a renewable resource • Many devices use photovoltaic cells • Example: cars
How Solar Cells Work • Two layers of semiconducting material between two layers of conducting metal • One layer of semiconductor is rich in electrons; one is poor in electrons
How Solar Cells Work • When sunlight strikes a solar cell, electrons are ejected from the electron-rich semiconductor. These electrons can travel in a closed circuit back to the electron-poor semiconductor
Parabolic Troughs • Focuses sunlight on a tube containing heat-absorbing fluid such as synthetic oil or liquid salt • Used in remote areas where electricity is hard to get • Best forms focus solar power into a receiver • Heated fluid is circulated through a boiler to make steam • Used in turbines
Energy from Water • Steam can move a turbine • Running water can be used the same way • GPE of water is increased if a dam is used • GPE is released when water flows through tunnels at the base
Energy from Water • Rushing water spins a turbine, which rotates the shaft of an electric generator to produce electricity
Hydroelectricity • Electricity produced from moving water • 8% of electrical energy in the US made by hydroelectric power plants • Very efficient with little pollution • Reservoirs created by dams for hydroelectric power can be used for drinking water and crops • Electricity is cheap after initial setup costs
Energy from Oceans • Every day ocean levels rise and fall • These tides can be used for hydroelectric power • Water is trapped behind a dam • At low tide, water flows back out to sea using turbines to generate electricity • Tide differences are limiting, only a few places on earth have large enough tidal differences • Waves and ocean currents can also be used
