Section 1: Fossil Fuels

• Using Energy

  • Energy is used in many ways.

  • To use energy means to transform one form of energy to another form of energy that can perform a useful function.

  • Sometimes energy is transformed into a form that isn’t useful.

  • More energy is used in the United States than in any other country in the world.

• Making Fossil Fuels

  • Fossil Fuels: Fuels such as petroleum, or oil, natural gas, and coal; are formed from the decaying remains of ancient plants and animals.

  • When fossil fuels are burned, carbon and hydrogen atoms combine with oxygen molecules in the air to form carbon dioxide and water molecules.

    • This process converts the chemical potential energy that is stored in the chemical bonds between atoms to heat and light.

    • Compared to other fuels such as wood, the chemical energy that is stored in fossil fuels is more concentrated.

• Petroleum: a highly flammable liquid formed by decayed ancient organisms, such as microscopic plankton and algae.

  • Petroleum is a mixture of thousands of chemical compounds

  • The different hydrocarbon molecules found in petroleum have different numbers and arrangements of carbon and hydrogen atoms

  • The many different compounds that are found in petroleum are separated in a process called fractional distillation.

  • Not all of the products obtained from petroleum are burned to produce energy.

• Natural Gas

  • The chemical processes that produce petroleum as ancient organisms decay also produce gaseous compounds called natural gas.

  • Natural gas is composed mostly of methane, CH4, but it also contains other hydrocarbon gases such as propane, C3H8, and butane, C4H10.

  • Natural gas is burned to provide energy for cooking, heating, and manufacturing.

  • Natural gas contains more energy per kilogram than petroleum or coal does.

• Coal

  • Coal is a solid fossil fuel that is found in mines underground.

  • Coal mines usually are located deep underground.

  • About 90 percent of all the coal that is used in the United States is burned by power plants to generate electricity.

  • Coal mines were once the sites of ancient swamps.

    • Coal formed from the organic material that was deposited as the plants that lived in these swamps died.

  • Coal also is a complex mixture of hydrocarbons and other chemical compounds.

• Generating Electricity

  • In the first stage, fuel is burned in a boiler or combustion chamber, and it releases thermal energy.

  • In the second stage, this thermal energy heats water and produces steam under high pressure.

  • In the third stage, the steam strikes the blades of a turbine, causing it to spin.

  • In the fourth stage, electric current is produced when the spinning turbine shaft rotates magnets inside the generator.

  • In the final stage, the electric current is transmitted to homes, schools, and businesses through power lines.

  • Fossil fuels are burned to generate electricity in a power plant.

• Efficiency of Power Plants

  • When fossil fuels are burned to produce electricity, not all the chemical energy in the fuel is converted to electrical energy.

  • The overall efficiency of the entire process is given by multiplying the efficiencies of each stage of the process

• The Costs of Using Fossil Fuels

  • Although fossil fuels are a useful source of energy for generating electricity and providing the power for transportation, their use has some undesirable side effects.

    • When petroleum products and coal are burned, smoke is given off that contains small particles called particulates. These particulates cause breathing problems for some people.

  • The most abundant fossil fuel is coal, but coal contains even more impurities than oil or natural gas.

  • Miners risk being killed or injured, and some suffer from lung diseases caused by breathing coal dust over long periods of time.

• Nonrenewable Resources: resources that cannot be replaced by natural processes as quickly as they are used.

  • As the production of energy from fossil fuels continues, the remaining reserves of fossil fuels will decrease.

  • Fossil fuels will become more difficult to obtain, causing them to become more costly in the future.

• Conserving Fossil Fuels

  • Even as reserves of fossil fuels decrease and they become more costly, the demand for energy continues to increase as the world’s population increases.

    • One way to meet these energy demands would be to reduce the use of fossil fuels and obtain energy from other sources.

Section 2: Nuclear Energy

• Using Nuclear Energy

  • A nuclear power plant generates electricity using the energy released in nuclear fission. Each of the domes contain a nuclear reactor. A cooling tower is on the left.

  • Energy is released when the nucleus of an atom breaks apart.

    • In this process, called nuclear fission, an extremely small amount of mass is converted into an enormous amount of energy.

• Nuclear Reactor: uses the energy from controlled nuclear reactions to generate electricity.

  • The core of a nuclear reactor contains the fuel rod bundles. Control rods that absorb neutrons are inserted between the fuel rod bundles. Water or another coolant is pumped through the core to remove the heat produced by the fission reaction.

  • Only certain elements have nuclei that can undergo fission.

    • Naturally occurring uranium contains an iso- tope, U-235, whose nucleus can split apart.

  • The reactor core contains uranium dioxide fuel in the form of tiny pellets.

    • The pellets are about the size of a pencil eraser and are placed end to end in a tube.

    • Nuclear fuel pellets are stacked together to form fuel rods. The fuel rods are bundled together, and the bundle is covered with a metal alloy.

  • When a neutron strikes the nucleus of a U-235 atom, the nucleus splits apart into two smaller nuclei. In the process two or three neutrons also are emitted. The smaller nuclei are called fission products.

  • Because every uranium atom that splits apart releases neutrons that cause other uranium atoms to split apart, this process is called a nuclear chain reaction.

  • Nuclear chain reactions take place in a matter of milliseconds. If the process isn’t controlled, the chain reaction will release energy explosively rather than releasing energy at a constant rate.

    • To control the chain reaction, some of the neutrons that are released when U-235 splits apart must be prevented from striking other U-235 nuclei.

• Nuclear Power Plants

  • Nuclear fission reactors produce electricity in much the same way that conventional power plants do.

  • A nuclear power plant uses the heat produced by nuclear fission in its core to produce steam. The steam turns an electric generator.

  • The overall efficiency of nuclear power plants is about 35 percent, similar to that of fossil fuel power plants.

• The Risks of Nuclear Power

  • Producing energy from nuclear fission has some disadvantages.

    • Nuclear power plants do not produce the air pollutants that are released by fossil-fuel burning power plants.

  • The mining of the uranium can cause environmental damage.

  • One of the most serious risks of nuclear power is the escape of harmful radiation from power plants.

• The Disposal of Nuclear Waste

  • After about three years, not enough fissionable U-235 is left in the fuel pellets in the reactor core to sustain the chain reaction.

  • Nuclear Waste: any radioactive by-product that results when radioactive materials are used.

  • Low-level nuclear wastes usually contain a small amount of radioactive material.

  • Products of some medical and industrial processes are low-level wastes, including items of clothing used in handling radioactive materials.

  • High-level nuclear waste is generated in nuclear power plants and by nuclear weapons programs.

    • Many of the radioactive materials in high-level nuclear waste have short half-lives.

    • One method proposed for the disposal of high-level waste is to seal the waste in ceramic glass, which is placed in protective metal-alloy containers

• Nuclear Fission

  • The Sun gives off a tremendous amount of energy through a process called thermonuclear fusion

    • Thermonuclear fusion is the joining together of small nuclei at high temperatures

  • In nuclear fusion, two smaller nuclei join together to form a larger nucleus. Energy is released in the process.

  • Fusion is the most concentrated energy source known.

  • An advantage of producing energy using nuclear fusion is that the process uses hydrogen as fuel.

  • One disadvantage of fusion is that it occurs only at temperatures of millions of degrees Celsius.

  • Another problem is how to contain a reaction that occurs at such extreme conditions.

Section 3: Renewable Energy Sources

• Energy Options

  • The demand for energy increases continually, but supplies of fossil fuels are decreasing.

  • Some alternative energy sources are renewable resources.

  • Renewable Resource: an energy source that is replaced nearly as quickly as it is used.

• Energy From the Sun

  • The average amount of solar energy that falls on the United States in one day is more than the total amount of energy used in the United States in one year

  • Photovoltaic Cell: converts radiant energy from the Sun directly into electrical energy.

    • Photovoltaic cells also are called solar cells.

  • Solar cells are made of two layers of semiconductor materials sandwiched between two layers of conducting metal

  • When sunlight strikes the surface of the solar cell, electrons flow through an electrical circuit from the electron-rich semiconductor to the electron-poor material.

  • Producing large amounts of electrical energy using solar cells is more expensive than producing electrical energy using fossil fuels.

  • Currently, the most promising solar technologies are those that concentrate the solar power into a receiver.

    • One such system is called the parabolic trough.

• Energy from Water

  • Hydroelectricity: Electricity produced from the energy of moving water

  • Hydroelectric power plants are an efficient way to produce electricity with almost no pollution.

  • Because no exchange of heat is involved in producing steam to spin a turbine, hydroelectric power plants are almost twice as efficient as fossil fuel or nuclear power plants.

  • Another advantage is that the bodies of water held back by dams can form lakes that can provide water for drinking and crop irrigation.

  • Artificial dams can disturb the balance of natural ecosystems.

• Energy From the Tides

  • The gravity of the Moon and Sun causes bulges in Earth’s oceans.

  • As Earth rotates, the two bulges of ocean water move westward.

  • Hydroelectric power can be generated by these ocean tides.

  • Tidal energy is nearly pollution free.

  • The efficiency of a tidal power plant is similar to that of a conventional hydroelectric power plant.

  • Only a few places on Earth have large enough differences between high and low tides for tidal energy to be a useful energy source.

• Harnessing the Wind

  • Windmills use the energy of the wind to pump water.

  • Windmills also can use the energy of the wind to generate electricity.

  • Research is underway to improve the design of wind generators and increase their efficiency.

  • Other disadvantages of wind energy are that windmills can be noisy and change the appearance of a landscape.

• Energy From Inside Earth

  • Heat is generated within Earth by the decay of radioactive elements.

    • This heat is called geothermal heat.

  • Geothermal heat causes the rock beneath Earth’s crust to soften and melt.

  • Geothermal Energy: The thermal energy that is contained in hot magma

  • Geothermal energy also can be used to generate electricity.

  • The efficiency of geothermal power plants is about 16 percent.

  • Although geothermal power plants can release some gases containing sulfur compounds, pumping the water created by the condensed steam back into Earth can help reduce this pollution.

• Alternative Fuels

  • The use of fossil fuels would be greatly reduced if cars could run on other fuels or sources of energy

  • Hybrid cars use both electric motors and gasoline engines.

  • Hydrogen gas is another possible alternative fuel.

  • Biomass: renewable organic matter, such as wood, sugarcane fibers, rice hulls, and animal manure.