chapter 9: energy sources -...

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sections

1 Fossil Fuels

2 Nuclear Energy

3 Renewable Energy SourcesLab Solar HeatingLab How much does energyreally cost?

Virtual Lab How much electrici-ty is used in a house?

That’s a lot of kilowatts!Look closely at this photo. Can you identifyat least three items that require energy tooperate? The welding torches require energyto join the pieces of the car together. Therobots require energy to assemble the pieces.When the car is finished, energy will berequired to operate the car.

Describe how your day would bedifferent if the electric power were off all day.Science Journal

Energy Sources

Sandy Felsenthal/CORBIS

Heating with Solar EnergyThe Sun constantly bathes our planet withenormous amounts of energy. This energycan be captured and used to make electricity,heat homes, and provide hot water. How canthe Sun’s energy be used to heat water?

1. Use scissors to poke a small hole in thecenter of two coffee can lids.

2. Fill a coffee can that has been paintedblack with water at room temperature.Snap on the lid and push a thermometerthrough the hole in the lid. Record thetemperature.

3. Repeat step 2 using the coffee can thathas been painted white.

4. Place both cans in direct sunlight. After 15 min, record the temperature of thewater in both cans again.

5. Think Critically Write a paragraphexplaining why the temperature changediffered between the two cans.

Start-Up Activities

Preview this chapter’s contentand activities atgpscience.com

Energy Sources There aremany sources of energy. Makethe following Foldable to help

you organize information about various types ofenergy sources.

Fold a sheet of paper in half length-wise. Make the back edge about 5 cmlonger than the front edge.

Turn the paper sothe fold is on thebottom. Then foldit into thirds.

Unfold and cut only the top layeralong both folds to make three tabs.

Label the Foldable as shown.

Summarize As you read this chapter,summarize important information abouteach type of energy source under theappropriate tab.

STEP 4

STEP 3

STEP 2

STEP 1

Energy Sources

FossilFuels

AlternativeSources

NuclearEnergy

Sandy Felsenthal/CORBIS

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256 CHAPTER 9 Energy Sources

Using EnergyHow many different ways have you used energy today? You

can see energy being used in many ways, throughout the day,such as those shown in Figure 1. Furnaces and stoves use ther-mal energy to heat buildings and cook food. Air conditionersuse electrical energy to move thermal energy outdoors. Cars andother vehicles use mechanical energy to carry people and mate-rials from one part of the country to another.

Transforming Energy According to the law of conservationof energy, energy cannot be created or destroyed. Energy canonly be transformed, or converted, from one form to another.To use energy means to transform one form of energy toanother form of energy that can perform a useful function. For

example, energy is used when the chemical energyin fuels is transformed into thermal energy that isused to heat your home.

Sometimes energy is transformed into a formthat isn’t useful. For example, when an electric cur-rent flows through power lines, about 10 percent ofthe electrical energy is changed to thermal energy.This reduces the amount of useful electrical energythat is delivered to homes, schools, and businesses.

Fossil Fuels

Automobiles burn gasolineto provide energy.

Power lines like these carry the electricalenergy you use every day.

Figure 1 Energy is used inmany ways.

Reading Guide

■ Discuss properties and uses offossil fuels.

■ Explain how fossil fuels areformed.

■ Describe how the chemicalenergy in fossil fuels is convertedinto electrical energy.

Fossil fuels are used to generate mostof the energy you use every day.

Review Vocabularychemical potential energy: theenergy stored in the chemical bondsbetween atoms in molecules

New Vocabulary

• fossil fuel

• petroleum

• nonrenewable resource

(t)James Sugar/Black Star, (b)Bill Heinsohn/Stone/Getty Images

SECTION 1 Fossil Fuels 257

Energy Use in the UnitedStates More energy is used inthe United States than in any othercountry in the world. Figure 2shows energy usage in the UnitedStates. About 20 percent of theenergy is used in homes for heat-ing and cooling, to run appliances,and to provide lighting and hotwater. About 27 percent is used fortransportation powering vehiclessuch as cars, trucks, and aircraft.Another 16 percent is used by businesses to heat, cool, and lightstores, shops, and office buildings. Finally, about 37 percent of thisenergy is used by industry and agriculture to manufacture prod-ucts and produce food. Figure 2 also shows the main sources ofthe energy used in the United States. Almost 85 percent of theenergy used in the United States comes from burning petroleum,natural gas, and coal. Nuclear power plants provide about eightpercent of the energy used in the United States.

Making Fossil FuelsIn one hour of freeway driving a car might use several gallons

of gasoline. It may be hard to believe that it took millions of yearsto make the fuels that are used to produce electricity, provideheat, and transport people and materials. Figure 4 on the nextpage shows how coal, petroleum, and natural gas are formed bythe decay of ancient plants and animals. Fuels suchas petroleum, or oil, natural gas, and coal are calledfossil fuels because they are formed from thedecaying remains of ancient plants and animals.

Concentrated Energy Sources When fossilfuels are burned, carbon and hydrogen atomscombine with oxygen molecules in the air to formcarbon dioxide and water molecules. This processconverts the chemical potential energy that isstored in the chemical bonds between atoms toheat and light. Compared to other fuels such aswood, the chemical energy that is stored in fossilfuels is more concentrated. For example, burning1 kg of coal releases two to three times as muchenergy as burning 1 kg of wood. Figure 3 showsthe amount of energy that is produced by burningdifferent fossil fuels.

Energy Content of Fuels

Ener

gy

con

ten

t p

er g

ram

(jou

les)

12,000

36,000

24,000

48,000

Type of Fuel

Woo

d

Coal

Gas

olin

e

Nat

ural

gas

Figure 3 The bar graph shows theamount of energy released by burn-ing one gram of four different fuels.Determine the ratio of the energycontent of natural gas to the energycontent of wood.

Residential20%

Industrial37%

Business16%

Transportation27%

Petroleum39%

Coal23%

Natural gas23%

Biomass and others 3%

Hydroelectric 4%

Nuclear8%

Energy Usage Sources of Energy

Figure 2 These circle graphsshow where energy is used in theUnited States and sources of thisenergy.

Figure 4

VISUALIZING THE FORMATION OF FOSSIL FUELS


O il and natural gas form when organic matter on the ocean floor, graduallyburied under additional layers of sediment, is chemically changed by heatand crushing pressure. The oil and gas may bubble to the surface or become

trapped beneath a dense rock layer. Coal forms when peat—partially decomposedvegetation—is compressed by overlying sediments and transformed first into lignite (soft brown coal) and then into harder, bituminous (buh TYEW muh nus)coal. These two processes are shown below.

Layer of sedimentcontaining remainsof dead marineorganisms

Ocean

Old ocean bed

Overlyinglayers ofsediment

Oil and natural gasformed by heat, pressure,and chemical reactions

OceanLand

Sediment Layer of rock

Oil and gas

Vegetation

Peat

New layers of overlying sediment

Increasingpressure andtemperature

Lignite Bituminous coal

New layers of overlyingsediment

HOW COAL IS FORMED

HOW OIL AND NATURAL GAS ARE FORMED

Increasingpressure andtemperature

Layer of rock

PetroleumMillions of gallons of petroleum, or crude oil, are pumped

every day from wells deep in Earth’s crust. Petroleum is a highlyflammable liquid formed by decayed ancient organisms, such as microscopic plankton and algae. Petroleum is a mixture ofthousands of chemical compounds. Most of these compoundsare hydrocarbons, which means their molecules contain onlycarbon atoms and hydrogen atoms.

Separating Hydrocarbons The different hydrocarbonmolecules found in petroleum have different numbers andarrangements of carbon and hydrogen atoms. The compositionand structure of hydrocarbons determines their properties.

The many different compounds that are found in petroleumare separated in a process called fractional distillation. This sep-aration occurs in the tall towers of oil-refinery plants. First,crude oil is pumped into the bottom of the tower and heated.The chemical compounds in the crude oil boil and vaporizeaccording to their individual boiling points. Materials with thelowest boiling points rise to the top of the tower as vapor and arecollected. Hydrocarbons with high boiling points, such asasphalt and some types of waxes, remain liquid and are drainedoff through the bottom of the tower.

What is fractional distillation used for?

Other Uses for Petroleum Not all of the products obtainedfrom petroleum are burned to produce energy. About 15 percentof the petroleum-based substances that are used in the UnitedStates go toward nonfuel uses. Look around at the materials inyour home or classroom. Do you see any plastics? In addition tofuels, plastics and synthetic fabrics are made from the hydrocar-bons found in crude petroleum. Also, lubricants such as greaseand motor oil, as well as the asphalt used in surfacing roads, areobtained from petroleum. Some synthetic materials producedfrom petroleum are shown in Figure 5.

Designing an EfficientWater HeaterProcedure

1. Measure and record themass of a candle.

2. Measure 50 mL of waterinto a beaker. Record thetemperature of the water.

3. Use the lighted candle toincrease the temperatureof the water by 10°C. Putout the candle and meas-ure its mass again.

4. Repeat steps 1 to 3 with analuminum chimney sur-rounding the candle to helpdirect the heat upward.

Analysis1. Compare the mass change

in the two trials. Does asmaller or larger masschange in the candle showgreater efficiency?

2. Gas burners are used toheat hot-water tanks. Whatmust be considered in thedesign of these heaters?


Figure 5 The objects shown here aremade from chemical compounds foundin petroleum.Identify four objects in your classroomthat are made from petroleum.

Amanita Pictures

Natural GasThe chemical processes that produce petroleum as ancient

organisms decay also produce gaseous compounds called naturalgas. These compounds rise to the top of the petroleum deposit andare trapped there. 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 energyfor cooking, heating, and manufacturing. About one fourth of theenergy consumed in the United States comes from burning natu-ral gas. There’s a good chance that your home has a stove, furnace,hot-water heater, or clothes drier that uses natural gas.

Natural gas contains more energy per kilogram than petro-leum or coal does. It also burns more cleanly than other fossilfuels, produces fewer pollutants, and leaves no residue such as ash.

CoalCoal is a solid fossil fuel that is found in mines underground,

such as the one shown in Figure 6. In the first half of the twen-tieth century, most houses in the United States were heated byburning coal. In fact, during this time, coal provided more thanhalf of the energy that was used in the United States. Now,almost two-thirds of the energy used comes from petroleumand natural gas, and only about one-fourth comes from coal.About 90 percent of all the coal that is used in the United Statesis burned by power plants to generate electricity.

Figure 6 Coal mines usually arelocated deep underground.


Fuel Steam

Steam

Water

Water

Turbine

Watertank

Intake pipe

Coolingwater

Stage 1The chemical energy in thefossil fuel isconverted to thermal energy as the fuel is burned in theboiler. Onlyabout 60 percent of the available chemical energy is convertedinto thermal energy.

Stage 2 The thermalenergy heats water and produces steam. This stage is 90percent efficient.

Stage 3 The steamat high pressurestrikes the bladesof a turbine and causes it to spin. This stage is 75percent efficient.

(t)Digital Vision/PictureQuest, (b)Doug Martin

Generator

Transformer

Power linesStage 4 The rotating turbinespins an electric generator. Ninety-five percent of the mechanical energy in therotating turbine is convertedinto electrical energy.

Stage 5 Electrical current istransmitted along power lines. Electrical resistance convertssome of the electrical energyto thermal energy. This stage is 90 percent efficient. Figure 8 Fossil fuels are burned to

generate electricity in a power plant. Determine which stage in thisprocess is the most inefficient.


Origin of Coal Coal mines were once the sites ofancient swamps. Coal formed from the organic materialthat was deposited as the plants that lived in theseswamps died. Worldwide, the amount of coal that ispotentially available is estimated to be 20 to 40 timesgreater than the supply of petroleum.

Coal also is a complex mixture of hydrocarbons andother chemical compounds. Compared to petroleumand natural gas, coal contains more impurities, such assulfur and nitrogen compounds. As a result, more pollu-tants, such as sulfur dioxide and nitrogen oxides, areproduced when coal is burned.

Generating ElectricityFigure 7 shows that almost 70 percent of the electrical

energy used in the United States is produced by burning fossilfuels. How is the chemical energy contained in fossil fuels con-verted to electrical energy in an electric power station?

The process is shown in Figure 8. In the first stage, fuel isburned in a boiler or combustion chamber, and it releases ther-mal energy. In the second stage, this thermal energy heats waterand produces steam under high pressure. In the third stage, thesteam strikes the blades of a turbine, causing it to spin. The shaftof the turbine is connected to an electric generator. In the fourthstage, electric current is produced when the spinning turbineshaft rotates magnets inside the generator. In the final stage,the electric current is transmitted to homes, schools, andbusinesses through power lines.

Nuclear power20%

Coal51%

Hydroelectric8%

Natural gas14%

Petroleum4%

Sources of Electricity

Other3%

Figure 7 This circle graphshows the percentage of electricitygenerated in the United States thatcomes from various energy sources.


Efficiency of PowerPlants

When fossil fuels are burned toproduce electricity, not all the chemicalenergy in the fuel is converted to electri-cal energy. In every stage of the process,some energy is converted into forms ofenergy that can’t be used.

The overall efficiency of the entireprocess is given by multiplying the effi-ciencies of each stage of the processshown in Table 1. If you were to do this,you’d find that the resulting overall effi-ciency is only about 35 percent. Thismeans that only about 35 percent of theenergy contained in the fossil fuels is

delivered to homes, schools, and businesses as electrical energy.The other 65 percent is converted mainly into thermal energywhen the chemical energy in fuel is transformed into electricalenergy that is delivered to energy users.

The Costs of Using Fossil FuelsAlthough fossil fuels are a useful source of energy for gener-

ating electricity and providing the power for transportation,their use has some undesirable side effects. When petroleumproducts and coal are burned, smoke is given off that containssmall particles called particulates. These particulates causebreathing problems for some people. Burning fossil fuels alsoreleases carbon dioxide. Figure 9 shows how the carbon dioxideconcentration in the atmosphere has increased from 1960 to2000. One consequence of increasing the atmospheric carbondioxide concentration could be to cause Earth’s surface temper-ature to increase.

Using Coal The most abundant fossil fuel is coal, but coalcontains even more impurities than oil or natu-ral gas. Many electric power plants that burncoal remove some of these pollutants beforethey are released into the atmosphere.Removing sulfur dioxide, for example, helps toprevent the formation of compounds that mightcause acid rain. Mining coal also can be danger-ous. Miners risk being killed or injured, andsome suffer from lung diseases caused bybreathing coal dust over long periods of time.

Atmospheric CO2 Concentration

CO2

con

cen

trat

ion

(par

ts p

er m

illio

n)

300

320

340

360

380

1960

1965

1970

1975

1980

1985

1990

1995

2000

Year

Table 1 Efficiency of Fossil Fuel Conversion

Process Efficiency (%)

Chemical to thermal energy 60

Conversion of water to steam 90

Steam-turning turbine 75

Turbine spins electric generator 95

Transmission through power lines 90

Overall efficiency 35

Figure 9 The carbon dioxideconcentration in Earth’s atmos-phere has been measured at MaunaLoa in Hawaii. From 1960 to 2000,the carbon dioxide concentrationhas increased by about 16 percent.


Self Check1. Describe the advantages and disadvantages of using

fossil fuels to generate electricity.

2. Explain how the different chemical compounds in crudeoil are separated.

3. Describe how fossil fuels are formed.

4. Name three materials that are derived from the chemi-cal compounds in petroleum.

5. Think Critically If fossil fuels are still forming, why arethey considered to be a nonrenewable resource?

SummaryUsing Energy

• Energy cannot be created or destroyed, butcan only be transformed from one form toanother.

Fossil Fuels

• Petroleum, natural gas, and coal are fossilfuels formed by the decay of ancient plantsand animals.

• Petroleum is a mixture of thousands of chemical compounds, most of which arehydrocarbons.

• About 90 percent of all coal used in the UnitedStates is burned by power plants to produceelectricity.

Generating Electricity

• Power plants burn fossil fuels to producesteam that spins turbines attached to electricgenerators.

6. Interpret a Graph According to the graph in Figure 9,by how many parts per million did the concentrationof atmospheric carbon dioxide increase from 1960 to2000?

7. Use a Table In Table 1, if the efficiency of convertingchemical to thermal energy was 90 percent, what would be the overall efficiency be?

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Nonrenewable ResourcesAll fossil fuels are nonrenewable

resources, which means they are resourcesthat cannot be replaced by natural processesas quickly as they are used. Therefore, fossilfuel reserves are decreasing at the same timethat population and industrial demands areincreasing. Figure 10 shows how the pro-duction of oil might decline over the next50 years as oil reserves are used up. As theproduction of energy from fossil fuels con-tinues, the remaining reserves of fossil fuelswill decrease. Fossil fuels will become moredifficult to obtain, causing them to becomemore 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 theworld’s population increases. One way to meet these energydemands would be to reduce the use of fossil fuels and obtainenergy from other sources.

Global Oil Production

2050203020101990197019501930

5

10

15

20

25

30

0

Oil

pro

du

ctio

n (b

illio

ns

of b

arre

ls)

Year

Figure 10 Some predictionsshow that worldwide oil produc-tion will peak by 2005 and thendecline rapidly over the following50 years.

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Using Nuclear EnergyOver the past several decades, electric power plants have been

developed that generate electricity without burning fossil fuels.Some of these power plants, such as the one shown in Figure 11,convert nuclear energy to electrical energy. Energy is releasedwhen the nucleus of an atom breaks apart. In this process, callednuclear fission, an extremely small amount of mass is convertedinto an enormous amount of energy. Today almost 20 percent ofall the electricity produced in the United States comes fromnuclear power plants. Overall, nuclear power plants produceabout eight percent of all the energy consumed in the UnitedStates. In 2003, there were 104 nuclear reactors producing elec-tricity at 65 nuclear power plants in the United States.

Nuclear ReactorsA nuclear reactor uses the energy from controlled

nuclear reactions to generate electricity. Althoughnuclear reactors vary in design, all have some parts incommon, as shown in Figure 12. They contain a fuelthat can be made to undergo nuclear fission; they con-tain control rods that are used to control the nuclearreactions; and they have a cooling system that keeps thereactor from being damaged by the heat produced. Theactual fission of the radioactive fuel occurs in a relativelysmall part of the reactor known as the core.

Nuclear Energy

Figure 11 A nuclear powerplant generates electricity usingthe energy released in nuclear fis-sion. Each of the domes contain anuclear reactor. A cooling tower ison the left.

Reading Guide

■ Explain how a nuclear reactorconverts nuclear energy to ther-mal energy.

■ Describe advantages and disad-vantages of using nuclear energyto produce electricity.

■ Discuss nuclear fusion as a possi-ble energy source.

Using nuclear energy to produceelectricity can help reduce the use offossil fuels. However, like all energysources, the use of nuclear energyhas advantages and disadvantages.

Review Vocabularynuclear fission: the process of split-ting an atomic nucleus into two ormore nuclei with smaller masses

New Vocabulary

• nuclear reactor

• nuclear waste

Robert Essel/The Stock Market/CORBIS

Nuclear Fuel Only certain elements have nuclei that canundergo fission. Naturally occurring uranium contains an iso-tope, U-235, whose nucleus can split apart. As a result, the fuelthat is used in a nuclear reactor is usually uranium dioxide.Naturally occurring uranium contains only about 0.7 percent ofthe U-235 isotope. In a reactor, the uranium usually is enrichedso that it contains three percent to fivepercent U-235.

The Reactor Core The reactor corecontains uranium dioxide fuel in theform of tiny pellets like the ones inFigure 13. The pellets are about the sizeof a pencil eraser and are placed end toend in a tube. The tubes are then bun-dled and covered with a metal alloy, asshown in Figure 13. The core of a typi-cal reactor contains about a hundredthousand kilograms of uranium inhundreds of fuel rods. For every kilo-gram of uranium that undergoes fissionin the core, 1 g of matter is convertedinto energy. The energy released by thisgram of matter is equivalent to theenergy released by burning more than3 million kg of coal.

Concreteshield

Steelvessel

Coolingwater

Heatedwater

Reactor core

Controlrods

Fuelrod

bundles

Fuelpellets

FPO

Fuelrod

Fuel-rodbundle

SECTION 2 Nuclear Energy 265

Figure 12 The core of a nuclear reactor contains thefuel rod bundles. Control rods that absorb neutrons areinserted between the fuel rod bundles. Water or anothercoolant is pumped through the core to remove the heatproduced by the fission reaction.

Figure 13 Nuclear fuel pelletsare stacked together to form fuelrods. The fuel rods are bundledtogether, and the bundle is covered with a metal alloy.

Photo Researchers

Uranium-Lead DatingUranium is used to deter-mine the age of rocks. Asuranium decays into leadat a constant rate, the ageof a rock can be found bycomparing the amount ofuranium to the amountof lead produced. Uranium-lead dating is used by sci-entists to date rocks asold as 4.6 billion years.Research other methodsused to determine the ageof rocks.


� Neutron

Neutron

Neutron

Fission product

Fission product

U-235Nucleus

Energy

Energy

Figure 14 When a neutron strikes the nucleus of aU-235 atom, the nucleus splits apart into two smallernuclei. In the process two or three neutrons also areemitted. The smaller nuclei are called fission products.Explain what happens to the neutrons that are released in this reaction.

Nuclear Fission How does the nuclear reaction proceed inthe reactor core? Neutrons that are produced by the decay ofU-235 nuclei are absorbed by other U-235 nuclei. When a U-235nucleus absorbs a neutron, it splits into two smaller nuclei andtwo or three additional neutrons, as shown in Figure 14. Theseneutrons strike other U-235 nuclei, causing them to release twoor three more neutrons each when they split apart.

Because every uranium atom that splits apart releases neu-trons that cause other uranium atoms to split apart, this processis called a nuclear chain reaction. In the chain reaction involvingthe fission of uranium nuclei, the number of nuclei that are splitcan more than double at each stage of the process. As a result,an enormous number of nuclei can be split after only a smallnumber of stages. For example, if the number of nuclei involveddoubles at each stage, after only 50 stages more than a quadrillionnuclei might be split.

Nuclear chain reactions take place in a matter of millisec-onds. If the process isn’t controlled, the chain reaction willrelease energy explosively rather than releasing energy at aconstant rate.

What is a nuclear chain reaction?

Controlling the Chain Reaction To control the chain reac-tion, some of the neutrons that are released when U-235 splitsapart must be prevented from striking other U-235 nuclei. Theseneutrons are absorbed by rods containing boron or cadmiumthat are inserted into the reactor core. Moving these control rodsdeeper into the reactor causes them to absorb more neutrons andslow down the chain reaction. Eventually, only one of the neu-trons released in the fission of each of the U-235 nuclei strikesanother U-235 nucleus, and energy is released at a constant rate.


Nuclear Power Plants Nuclear fission reactors produce electricity in much the same

way that conventional power plants do. Figure 15 shows how anuclear reactor produces electricity. The thermal energy releasedin nuclear fission is used to heat water and produce steam. Thissteam then is used to drive a turbine that rotates an electric gen-erator. To transfer thermal energy from the reactor core to heatwater and produce steam, the core is immersed in a fluid coolant.The coolant absorbs heat from the core and is pumped through aheat exchanger. There thermal energy is transferred from thecoolant and boils water to produce steam. The overall efficiencyof nuclear power plants is about 35 percent, similar to that offossil fuel power plants.

The Risks of Nuclear PowerProducing energy from nuclear fission has some disadvan-

tages. Nuclear power plants do not produce the air pollutantsthat are released by fossil-fuel burning power plants. Also,nuclear power plants don’t produce carbon dioxide.

The nuclear generation of electricity, however, has its problems.The mining of the uranium can cause environmental damage.Water that is used as a coolant in the reactor core must cool beforeit is released into streams and rivers. Otherwise, the excess heatcould harm fish and other animals and plants in the water.

Pump

Control rod

Reactor core

PumpPump

Coolingwater

Boiler

Turbine

Containment shell

Generator

Condenser

High-pressure steam

Low-pressure steam

Figure 15 A nuclear powerplant uses the heat produced bynuclear fission in its core to pro-duce steam. The steam turns anelectric generator.

Ukraine The worst nuclearaccident in history occurredat the Chernobyl nuclearpower plant in the Ukrainein 1986. Many people in thearea suffered from radiationsickness. Use a map oratlas to find the locationof the Ukraine. Write adescription of the locationin your Science Journal.


The Release of Radioactivity Oneof the most serious risks of nuclearpower is the escape of harmful radiationfrom power plants. The fuel rods containradioactive elements with various half-lives. Some of these elements could causedamage to living organisms if they werereleased from the reactor core. Nuclearreactors have elaborate systems of safe-guards, strict safety precautions, andhighly trained workers in order to pre-vent accidents. In spite of this, accidentshave occurred.

For example, in 1986 in Chernobyl,Ukraine, an accident occurred when areactor core overheated during a safetytest. Materials in the core caught fire and

caused a chemical explosion that blew a hole in the reactor, asshown in Figure 16. This resulted in the release of radioactivematerials that were carried by winds and deposited over a largearea. As a result of the accident, 28 people died of acute radia-tion sickness. It is possible that 260,000 people might have beenexposed to levels of radiation that could affect their health.

In the United States, power plants are designed to preventaccidents such as the one that occurred at Chernobyl. But manypeople still are concerned that similar accidents are possible.

The Disposal of Nuclear WasteAfter about three years, not enough fissionable U-235 is left

in the fuel pellets in the reactor core to sustain the chain reac-tion. The spent fuel contains radioactive fission products inaddition to the remaining uranium. Nuclear waste is anyradioactive by-product that results when radioactive materialsare used.

Low-Level Waste Low-level nuclear wastes usually contain a small amount of radioactive material. They usually do notcontain radioactive materials with long half-lives. Products ofsome medical and industrial processes are low-level wastes,including items of clothing used in handling radioactive mate-rials. Low-level wastes also include used air filters from nuclearpower plants and discarded smoke detectors. Low-level wastesusually are sealed in containers and buried in trenches 30 mdeep at special locations. When dilute enough, low-level wastesometimes is released into the air or water.

Figure 16 An explosionoccurred at the Chernobyl reactorin the Ukraine after graphite con-trol rods caught fire. The explosionshattered the reactor’s roof.

Topic: Storing NuclearWastesVisit gpscience.com for Web linksto information about storingnuclear wastes.

Activity Obtain a map or sketchan outline of the United States.Mark the locations of the nuclearwaste sites that you found. Whatdo these locations have in com-mon? Why do you think theselocations were chosen over othersites that were closer to thenuclear waste generating sites?

AFP/CORBIS



High-Level Waste High-level nuclear waste isgenerated in nuclear power plants and by nuclearweapons programs. After spent fuel is removed froma reactor, it is stored in a deep pool of water, asshown in Figure 17. Many of the radioactive materi-als in high-level nuclear waste have short half-lives.However, the spent fuel also contains materials thatwill remain radioactive for tens of thousands ofyears. For this reason, the waste must be disposed ofin extremely durable and stable containers.

What is the difference between low-level and high-level nuclear wastes?

One method proposed for the disposal of high-level waste isto seal the waste in ceramic glass, which is placed in protectivemetal-alloy containers. The containers then are buried hundredsof meters below ground in stable rock formations or saltdeposits. It is hoped that this will keep the material from con-taminating the environment for thousands of years.

Can a contaminated radioactive site be reclaimed?

I n the early 1900s, with the discovery of radium, extensive miningfor the element began in the Denver, Colorado, area. Radium is a

radioactive element that was used to make watch dials and instru-ment panels that glowed in the dark. After World War I, the radiumindustry collapsed. The area was left contaminated with 97,000tons of radioactive soil and debris containing heavy metals andradium, which is now known to cause cancer. The soil was used asfill, foundation material, left in place, or mishandled.

Identifying the ProblemIn the 1980s, one area became known as the Denver Radium Superfund Site and

was cleaned up by the Environmental Protection Agency. The land then was reclaimedby a local commercial establishment.

Solving the Problem1. The contaminated soil was placed in one area and a protective cap was placed over it.

This area also was restricted from being used for residential homes. Explain why it isimportant for the protective cap to be maintained and why homes could not be builtin this area.

2. The advantages of cleaning up this site are economical, environmental, and social.Give an example of each.

Radium88Ra

(226)

Figure 17 Spent nuclear fuelrods are placed underwater afterthey are removed from the reactorcore. The water absorbs the nuclearradiation and prevents it fromescaping into the environment.

Tim Wright/CORBIS


Self Check1. Explain why a chain reaction occurs when uranium-235

undergoes fission.

2. Describe how the chain reaction in a nuclear reactor iscontrolled.

3. Compare the advantages and disadvantages of nuclearpower plants and those that burn fossil fuels.

4. Describe the advantages and disadvantages of usingnuclear fusion reactions as a source of energy.

5. Think Critically A research project produced 10 g ofnuclear waste with a short half-life. How would youclassify this waste and how would it be disposed of?

SummaryUsing Nuclear Energy

• Nuclear power plants produce about eightpercent of the energy used each year in theUnited States.

Nuclear Power Plants

• Nuclear reactors use the energy released inthe fission of U-235 to produce electricity.

• The energy released in the fission reaction isused to make steam. The steam drives a tur-bine that rotates an electric generator.

The Risks of Nuclear Energy

• Nuclear power generation produces high-levelnuclear wastes.

• Organisms could be damaged if radiation isreleased from the reactor.

• Nuclear waste is the radioactive by-productproduced by using radioactive materials.

6. Use Percentages Naturally occurring uranium contains 0.72 percent of the isotope uranium-235.What is the mass of uranium-235 in 2,000 kg of naturally-occurring uranium?

Nuclear FusionThe Sun gives off a tremen-

dous amount of energy througha process called thermonuclearfusion. Thermonuclear fusion isthe joining together of smallnuclei at high temperatures, asshown in Figure 18. In thisprocess, a small amount of massis converted into energy. Fusion

is the most concentrated energy source known.An advantage of producing energy using nuclear fusion is

that the process uses hydrogen as fuel. Hydrogen is abundant onEarth. Another advantage is that the product of the reaction ishelium. Helium is not radioactive and is chemically nonreactive.

One disadvantage of fusion is that it occurs only at temper-atures of millions of degrees Celsius. Research reactors oftenconsume more energy to reach and maintain these temperaturesthan they produce. Another problem is how to contain a reac-tion that occurs at such extreme conditions. Until solutions tothese and other problems are found, the use of nuclear fusion asan energy source is not practical.


Energy

He-4 nucleus

NeutronH-2 nucleus

H-3 nucleus

Figure 18 In nuclear fusion,two smaller nuclei join together toform a larger nucleus. Energy isreleased in the process. In the reac-tion shown here, two isotopes ofhydrogen come together to form ahelium nucleus.Identify the source of the energyreleased in a fusion reaction.


SECTION 3 Renewable Energy Sources 271

Renewable Energy Sources

Solarcell

Figure 19 This calculator uses asolar cell to produce the electricityit needs to operate.

Reading Guide

■ Analyze the need for alternateenergy sources.

■ Describe alternate methods forgenerating electricity.

■ Compare the advantages and dis-advantages of various alternateenergy sources.

The primary sources of energy in theUnited States are nonrenewable, soalternative energy sources need tobe explored.

Review Vocabularyradiant energy: the energy carriedby an electromagnetic wave

New Vocabulary

• renewable resource

• photovoltaic cell

• hydroelectricity

• geothermal energy

• biomass

Energy OptionsThe demand for energy increases continually, but supplies of

fossil fuels are decreasing. Using more nuclear reactors to pro-duce electricity will produce more high-level nuclear waste thathas to be disposed of safely. As a result, other sources of energythat can meet Earth’s increasing energy demands are beingdeveloped. Some alternative energy sources are renewableresources. A renewable resource is an energy source that isreplaced nearly as quickly as it is used.

Energy from the SunThe average amount of solar energy that falls on the United

States in one day is more than the total amount of energy used inthe United States in one year. Because only about one billionth ofthe Sun’s energy falls on Earth, and because the Sun is expectedto continue producing energy for several billion years, solarenergy cannot be used up. Solar energy is a renewable resource.

Many devices use solar energy for power including solar-powered calculators similar to the one in Figure 19. Thesedevices use a photovoltaic cell that converts radiant energyfrom the Sun directly into electrical energy. Photovoltaic cellsalso are called solar cells.

Amanita Pictures


Current

CurrentMetal

contact

Metalcontact

Electron-richsemiconductor

Electron-poorsemiconductor

Antireflectivecoating

Glass cover

Sunlight

A solar cell is made of two layers of semicon-ductor material.

When sunlight strikes a solar cell, electrons are ejected from the electron-rich semi-conductor. These electrons can travel in a closed circuit back to the electron-poor semiconductor.

Using Solar Power at HomeProcedure1. Cut a piece of cloth into

four equal sized pieces.2. Wet the pieces and wring

them out so they are thesame dampness.

3. Spread the pieces out todry—two pieces insideand two pieces outdoors.One piece of each setshould be in direct sunlightand one piece should be inthe shade.

4. In your Science Journal,record the time it takes foreach cloth piece to dry.

Analysis1. How long did it take for each

cloth piece to dry?2. What conditions determined

how quickly the cloth dried?3. Infer how you can use solar

energy in your home to conserve electricity.

How Solar Cells Work Solar cells are made of two layers ofsemiconductor materials sandwiched between two layers of con-ducting metal, as shown in Figure 20. One layer of semiconduc-tor is rich in electrons, while the other layer is electron poor.When sunlight strikes the surface of the solar cell, electrons flowthrough an electrical circuit from the electron-rich semiconduc-tor to the electron-poor material. This process of convertingradiant energy from the Sun directly to electrical energy is onlyabout 7 percent to 11 percent efficient.

Using Solar Energy Producing large amounts of electricalenergy using solar cells is more expensive than producing elec-trical energy using fossil fuels. However, in remote areas whereelectric distribution lines are not available, the use of solar cellsis a practical way of providing electrical power.

Currently, the most promising solar technologies are thosethat concentrate the solar power into a receiver. One such systemis called the parabolic trough. The trough focuses the sunlight ona tube that contains a heat-absorbing fluid such as synthetic oilor liquid salt. The heated fluid is circulated through a boilerwhere it generates steam to turn a turbine, generating electricity.

The worlds’ largest concentrating solar power plant is locatedin the Mojave Desert in California. This facility consists of nineunits that generate over 350 megawatts of power. These nineunits can generate enough electrical power to meet the needs ofapproximately 500,000 people. These units use natural gas as abackup power source for generating electricity at night and oncloudy days when solar energy is unavailable.

Figure 20 Solarcells convert radiantenergy from the Sunto electricity.Identify two devicesthat use solar cells forpower.


Energy from WaterJust as the expansion of

steam can turn an electricgenerator, rapidly movingwater can as well. The gravita-tional potential energy of thewater can be increased if thewater is retained by a highdam. This potential energy isreleased when the water flowsthrough tunnels near the baseof the dam. Figure 21 showshow the rushing water spins aturbine, which rotates the shaft of an electric generatorto produce electricity. Damsbuilt for this purpose arecalled hydroelectric dams.

Using Hydroelectricity Electricity produced from theenergy of moving water is called hydroelectricity. Currentlyabout 8 percent of the electrical energy used in the United Statesis produced by hydroelectric power plants. Hydroelectric powerplants are an efficient way to produce electricity with almost nopollution. Because no exchange of heat is involved in producingsteam to spin a turbine, hydroelectric power plants are almosttwice as efficient as fossil fuel or nuclear power plants.

Why are hydroelectric power plants moreefficient than fossil fuel power plants?

Another advantage is that the bodies of water heldback by dams can form lakes that can provide water fordrinking and crop irrigation. These lakes also can beused for boating and swimming. Also, after the initialcost of building a dam and a power plant, the electric-ity is relatively cheap.

However, artificial dams can disturb the balance ofnatural ecosystems. Some species of fish that live in theocean migrate back to the rivers in which they werehatched to breed. This migration can be blocked by dams,which causes a decline in the fish population. Fish ladders,such as those shown in Figure 22, have been designed toenable fish to migrate upstream past some dams. Also,some water sources suitable for a hydroelectric powerplant are located far from the regions needing power.

Dam

Generator

Reservoir

Turbine

Figure 21 The potential energyin water stored behind the dam isconverted to electrical energy in ahydroelectric power plant. Diagram the energy conversionsthat occur as a hydroelectric damproduces electrical energy.

Figure 22 Fish ladders enablefish to migrate upstream past dams.

S.K. Patrick/Tom Stack & Assoc.

Energy from the TidesThe gravity of the Moon and Sun causes

bulges in Earth’s oceans. As Earth rotates, thetwo bulges of ocean water move westward.Each day, the level of the ocean on a coast risesand falls continually. Hydroelectric power canbe generated by these ocean tides. As the tidecomes in, the moving water spins a turbine thatgenerates electricity. The water is then trappedbehind a dam. At low tide the water behind thedam flows back out to the ocean, spinning theturbines and generating electric power.

Tidal energy is nearly pollution free. Theefficiency of a tidal power plant is similar to

that of a conventional hydroelectric power plant. However, onlya few places on Earth have large enough differences betweenhigh and low tides for tidal energy to be a useful energy source.The only tidal power station in use in North America is atAnnapolis Royal, Nova Scotia, shown in Figure 23. Tidal energyprobably will be a limited source of energy in the future.

Harnessing the WindYou might have seen a windmill on a farm or pictures of

windmills in a book. These windmills use the energy of the windto pump water. Windmills also can use the energy of the wind togenerate electricity. Wind spins a propeller that is connected toan electric generator. Windmill farms, like the one shown inFigure 24, may contain several hundred windmills.

However, only a few places onEarth consistently have enough windto rely on wind power to meetenergy needs. Also, windmills areonly about 20 percent efficient onaverage. Research is underway toimprove the design of wind genera-tors and increase their efficiency.Other disadvantages of wind energyare that windmills can be noisy andchange the appearance of a land-scape. Also, they can disrupt themigration patterns of some birds.However, wind generators do notconsume any nonrenewable naturalresources, and they do not pollutethe atmosphere or water.

Figure 23 This tidal energyplant at Annapolis Royal, NovaScotia, generates 20 megawattsof electric power.

Figure 24 Wind energy is con-verted to electricity as the spinningpropeller turns a generator.

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Energy from Inside EarthEarth is not completely solid. Heat is gener-ated within Earth by the decay of radioac-

tive elements. This heat is called geothermal heat. Geothermalheat causes the rock beneath Earth’s crust to soften and melt.This hot molten rock is called magma. The thermal energy thatis contained in hot magma is called geothermal energy.

In some places, Earth’s crust has cracks or thin spots thatallow magma to rise near the surface. Active volcanoes, forexample, permit hot gases and magma from deep within Earthto escape. Perhaps you have seen a geyser, like Old Faithful inYellowstone National Park, shooting steam and hot water. Thewater that shoots from the geyser is heated by magma close toEarth’s surface. In some areas, this hot water can be pumpedinto houses to provide heat.

What two natural phenomena are caused bygeothermal heat?

Geothermal Power PlantsGeothermal energy also can beused to generate electricity, asshown in Figure 25. Wheremagma is close to the surface,the surrounding rocks are alsohot. A well is drilled and wateris pumped into the ground,where it makes contact with thehot rock and changes intosteam. The steam then returnsto the surface, where it is usedto rotate turbines that spin elec-tric generators.

The efficiency of geothermalpower plants is about 16 percent.Although geothermal powerplants can release some gasescontaining sulfur compounds,pumping the water created bythe condensed steam back intoEarth can help reduce thispollution. However, the use ofgeothermal energy is limited toareas where magma is relativelyclose to the surface.


Cooling tower / Condenser

GeneratorElectricityTurbine

Fractures in rockSteam

Magma

Pump

Figure 25 A geothermal powerplant converts geothermal energyto electrical energy. Water ischanged to steam by the hot rock.The steam is pumped to the surfacewhere it turns a turbine attached toan electric generator.

Topic: Geothermal EnergyVisit gpscience.com for Web linksto information about geothermalenergy.

Activity Using the informationthat you find write a paragraphdescribing why current facilitiesare located where they are.



Self Check1. Explain the need to develop and use alternative energy

sources.

2. Describe three ways that solar energy can be used.

3. Explain how the generation of electricity by hydroelec-tric, tidal, and wind sources are similar to each other.

4. Explain why geothermal energy is unlikely to become amajor energy source.

5. Think Critically What single energy source do mostenergy alternatives depend on, either directly orindirectly?

SummaryEnergy Options

• The development of alternative energysources can help reduce the use of fossil fuels.

Solar Energy

• Photovoltaic cells, or solar cells, convert radiantenergy from the Sun into electrical energy.

• Producing large amounts of energy from solarcells is more expensive than using fossil fuels.

Other Renewable Energy Sources

• Hydroelectric power plants convert the poten-tial energy in water to electrical energy.

• Tidal energy, wind energy, and geothermalenergy can be converted into electrical energy,but are useable only in certain locations.

• Alternative fuels such as hydrogen could beused to power cars, and biomass can beburned to provide heat.

6. Use Percentages A house uses solar cells that gener-ate 6.0 kW of electrical power to supply some of itsenergy needs. If the solar panels supply the housewith 40 percent of the power it needs, how muchpower does the house use?

Alternative Fuels The use of fossil fuels would be greatly

reduced if cars could run on other fuels orsources of energy. For example, cars havebeen developed that use electrical energysupplied by batteries as a power source.Hybrid cars use both electric motors andgasoline engines. Hydrogen gas is anotherpossible alternative fuel. It produces onlywater vapor when it burns and creates nopollution. Figure 26 shows a car that isequipped to use hydrogen as fuel.

Biomass Fuels Could any other mate-rials be used to heat water and produceelectricity like fossil fuels and nuclear fis-

sion? Biomass can be burned in the presence of oxygen to con-vert the stored chemical energy to thermal energy. Biomass isrenewable organic matter, such as wood, sugarcane fibers, ricehulls, and animal manure. Converting biomass is probably theoldest use of natural resources for meeting human energyneeds.


Figure 26 Hydrogen may oneday replace gasoline as a fuel forautomobiles. Burning hydrogenproduces water vapor, instead ofcarbon dioxide.

Martin Bond/Science Photo Library/Photo Researchers


Energy from the Sun is absorbed by Earth andmakes its temperature warmer. In a similarway, solar energy also is absorbed by solar col-lectors to heat water and buildings.

Real-World QuestionDoes the rate at which an object absorbs solarenergy depend on the color of the object?

Goals■ Demonstrate solar heating.■ Compare the effectiveness of heating items

of different colors.■ Graph your results.

Materialssmall cardboard boxesblack, white, and colored papertape or gluethermometerwatch with a second hand

Procedure1. Cover at least three small boxes with colored

paper. The colors should include black andwhite as well as at least one other color.

2. Copy the data table into your Science Journal.Replace Other color with whatever color youare using.

3. Place the three objects on a windowsill orother sunny spot and note the starting time.

4. Measure and record the temperature insideeach box at 2-min intervals for at least 10 min.

Conclude and Apply1. Graph your data using a line graph.

2. Describe the shapes of the lines on yourgraph. What color heated up the fastest?Which heated up the slowest?

3. Explain why the colored boxes heated atdifferent rates.

4. Infer Suppose you wanted to heat a tubof water using solar energy. Based on theresults of this activity, what color wouldyou want the tub to be? Explain.

5. Explain why you might want to wear awhite or light-colored shirt on a hot, sunny,summer day.

SSlar Heating

Compare your results with those of other students in your class. Discuss any differences found in your graphs,particularly if different colors were used by different groups.

LAB 277

Temperature Due to Different Colors

Color 2 4 6 8 10 min min min min min

Black

White

Other color

Do not write in this book.

Use the InternetUse the Internet

Real-World QuestionYou know that it costs money to produce energy. Using energy also can have an impact on the environment. For example, coal costsless than some other fuels. However, combustion is a chemical reac-tion that can produce pollutants, and burning coal produces morepollution than burning other fossil fuels, such as natural gas. Evenenergy sources, such as hydroelectric power, that don’t produce pollu-tion can have an impact on the environment. What are some of theenvironmental impacts of the evergy sources used in the UnitedStates? How can these environmental impacts be compared to thecost of the energy produced?

Make a Plan1. Research the various sources of energy used in different areas of

the United States and choose three energy sources to investigate.

2. Research the cost of the consumer of 1 kWh of electrical energygenerated by energy sources you have choosen.

3. Determine the effects each of the three energy sources has onthe environment.

4. Use your data to create a table show-ing the energy sources, and the energycost and environmental impact of eachenergy source.

5. Decide how you will evaluate theenvironmental impact of each of yourenergy sources.

6. Write a summary describing which ofyour three energy sources is the mostcost-effective for producing energy.Consider the cost of the energy andyour evaluation of the environmentalimpact in making your decision. Useinformation from your research tosupport your conclusions.

Goals■ Identify three energy

sources that people use.■ Determine the cost of

the energy produced byeach source.

■ Describe the environ-mental impact of eachsource.

Data Source

Visit gpscience.com/internet_lab for moreinformation about energysources and for data col-lected by other students.

How much does energy really co$t?

Tim

othy

Ful

ler

http://gpscience.com/internet_lab

Follow Your Plan1. Make sure your teacher approves your plan before you start.

2. Record your data in your Science Journal.

Analyze Your Data1. Of the energy sources you investigated, which is the most expensive to use? The

least expensive?

2. Which energy source do you think has the most impact on the environment?The least impact?

Conclude and Apply1. Explain Of the energy sources you investigated,

which is the least expensive energy source?Which is the best choice to use? Why or why not?

3. Explain Of the energy sources you investigated,how did the environmental impact of using thatenergy source influence your choice of the bestenergy solution?

4. Evaluate Which data support your decision?

LAB 279

Find this lab using the link below. Post your data in the table provided.Compare your data to those of otherstudents.

Energy Sources

Energy Source

Cost per Environmental kWh Impacts

Energy source 1

Energy source 2

Energy source 3

gpscience.com/internet_lab

Martin B. Withers/Frank Lane Picture Agency/CORBIS

Do not write in this book.

http://gpscience.com/internet_lab

M ost people agree that thanks to energysources, we have many things thatmake our quality of life better. Energy

runs our cars, lights our homes, and powers ourappliances. What many people don’t agree on iswhere that energy should come from.

Almost all of the world’s electric energy isproduced by thermal power plants. Most ofthese plants burn fossil fuels—such as coal, oil,and natural gas—to produce energy. Nuclearenergy is produced by fission, which is the split-ting of an atom’s nucleus. People in favor ofnuclear energy argue that, unlike fossil fuels,nuclear energy is nonpolluting.

Opponents counter, though, that the poisonous radioactive waste created in nuclearreactors qualifies as pollution—and will be lin-gering in the ground and water for hundreds ofthousands of years.

Supporters of nuclear energy also cite thespectacular efficiency of nuclear energy—onemetric ton of nuclear fuel produces the sameamount of energy as up to 3 million tons of coal.Opponents point out that uranium is in veryshort supply and, like fossil fuels, is likely to runout in the next 100 years.

Opponents worry that as utilities comeunder less government regulation, safety stan-dards will be ignored in the interest of profit.

This could result in more accidents like the onethat occurred at Chernobyl in the Ukraine.There, an explosion in the reactor core releasedradiation over a wide area.

Supporters counter that it will never be inthe best interests of those running nuclear plantsto relax safety standards since those safety stan-dards are the best safeguard of workers’ health.They cite the overall good safety record ofnuclear power plants.

This site at Yucca Mountain, Nevada, is thelocation of a proposed high-level nuclear wastestorage facility. Here radioactive materialswould be buried for tens of thousands of years.

SCIENCEANDSocietySCIENCE ISSUES

THAT AFFECTYOU!

Debate Form three teams and have each team defend one ofthe views presented here. If you need more information, go to theGlencoe Science Web site. “Debrief” after the debate. Did thearguments change your understanding of the issues?

For more information, visitgpscience.com/time

Reacting tkNuclear Energy

Dan Lamont/CORBIS

http://gpscience.com/time

Fossil Fuels

1. Fossil fuels include oil, natural gas,and coal.They formed from the buried remains ofplants and animals.

2. Fossil fuels canbe burned tosupply energyfor generatingelectricity.Petroleum alsois used to make plastics and synthetic fabrics.

3. Fossil fuels are nonrenewable energyresources. They can be replaced, but it takesmillions of years.

Nuclear Energy

1. A nuclear reactor transforms the energyfrom a controlled nuclear chain reaction toelectrical energy.

2. Nuclear wastes must be contained and dis-posed of carefully so radiation from nucleardecay will not leak into the environment.These low-level nuclear wastes are buried toprotect living organisms.

3. Nuclear fusion releases energy when twonuclei combine. Fusion only occurs at hightemperatures that are difficult to producein a laboratory.

Renewable Energy Sources

1. Alternative energy resources can be used tosupplement or replace nonrenewableenergy resources.

2. Other sources of energy for generating elec-tricity include hydroelectricity and solar,wind, tidal, and geothermal energy. Eachsource has its advantages and disadvan-tages. Also, some of these sources can dam-age the environment.

3. Although somealternative energysources produceless pollution thanfossil fuels do andare renewable, theiruse often is limitedto the regionswhere the energysource is available.For example, tidescan be used to generate electricity in coastal regions only.

4. It may be possible to use hydrogen as a fuelfor automobiles and other vehicles.Biomass, such as wood and other renewableorganic matter, has been used as fuel forthousands of years.

CHAPTER STUDY GUIDE 281gpscience.com/interactive_tutor

Use the Foldable that you made at the begin-ning of the chapter to help you review energy sources.

(tl)Amanita Pictures, (cr)Kathy Ferguson/PhotoEdit, Inc., (bl)US Department of Energy/Science Photo Library/Photo Researchers

http://gpscience.com/interactive_tutor

Complete each statement using a term from thevocabulary list above.

1. A(n) _________ uses the Sun to generateelectricity.

2. _________ makes use of thermal energyinside the Earth.

3. Energy produced by the rise and fall ofocean levels is a(n) _________.

4. _________ includes the following: oil,natural gas, and coal.

5. Fossil fuels are a(n) _________ becausethey are being used up faster than they arebeing made.

6. A special caution should be taken indisposing of _________.

Choose the word or phrase that best answersthe question.

7. Why are fossil fuels considered to benonrenewable resources?A) They are no longer being produced.B) They are in short supply.C) They are not being produced as fast as

they’re being used.D) They contain hydrocarbons.

8. To generate electricity, nuclear power plantsproduce which of the following?A) steam C) plutoniumB) carbon dioxide D) water

9. What is a major disadvantage of usingnuclear fusion reactors?A) use of hydrogen as fuelB) less radioactivity producedC) extremely high temperatures requiredD) use of only small nuclei

10. How are spent nuclear fuel rods usuallydisposed of?A) burying them in a community landfillB) storing them in a deep pool of waterC) burying them at the reactor siteD) releasing them into the air

11. How much energy in the United Statescomes from burning petroleum, naturalgas, and coal?A) 85% C) 65%B) 35% D) 25%

12. Solar cells would be more practical to useif they were which of the following?A) pollution free C) less expensiveB) nonrenewable D) larger

13. Which energy source uses water that isheated naturally by Earth’s internal heat?A) hydroelectricity C) tidal energyB) nuclear fission D) geothermal energy

14. What do hydrocarbons react with whenfossil fuels are burned?A) carbon dioxide C) oxygenB) carbon monoxide D) water

15. Which of the following is NOT a source ofnuclear waste?A) products of fission reactorsB) materials with short half-livesC) some medical and industrial productsD) products of coal-burning power plants

16. Which of the following is the source ofalmost all of Earth’s energy resources?A) plants C) magmaB) the Sun D) fossil fuels

282 CHAPTER REVIEW gpscience.com/vocabulary_puzzlemaker

biomass p. 276fossil fuel p. 257geothermal energy p. 275hydroelectricity p. 273nonrenewable resource

p. 263

nuclear reactor p. 264nuclear waste p. 268petroleum p. 259photovoltaic cell p. 271renewable resource p. 271

http://gpscience.com/vocabulary_puzzlemaker

17. Copy and complete the table belowdescribing possible effects of changes inthe normal operation of a nuclear reactor.

18. Copy and complete this concept map.

19. Infer why alternative energy resources aren’tmore widely used.

20. Infer whether fossil fuels should be con-served if renewable energy sources arebeing developed.

21. Infer Suppose new reserves of fossil fuelswere found and a way to burn these fuelswas developed that did not release pollu-tants and carbon dioxide into the atmos-phere. Should fossil fuels still beconserved? Explain

22. Explain why coal is considered a nonrenew-able energy source, but biomass, such aswood, is considered a renewable energysource.

23. Make a table listing two advantages and twodisadvantages for each of the followingenergy sources: fossil fuels, hydroelectric-ity, wind turbines, nuclear fission, solarcells, and geothermal energy.

24. Convert Units Crude oil is sold on theworld market in units called barrels. Abarrel of crude oil contains 42 gallons.If 1 gallon is 3.8 liters, how many litersare there in a barrel of crude oil?

Use the table below to answer question 25.

25. Use Percentages Nine of the top coal pro-ducing mines are located in Wyoming.Production information on two of themines is in the table above. A total ofabout 1.02 � 109 metric tons is pro-duced per year in the United States.What percentage do these two coalmines contribute to the total yearly coalproduction in the U.S.?

CHAPTER REVIEW 283gpscience.com/chapter_review

which are

Energy Sources

renewablesources

radiant toelectrical

Reactor Problems

Cause Effect

The cooling water isreleased hot.

The control rods areremoved.

The reactor core overheats and meltdown occurs.

can be can be

energy conversions

geothermalsolar cells hydroelectricity

nuclear tothermal

used fasterthan they are

replaced

energy conversions

fossil fuels nuclear fission

High-Production Coal Mines

Coal Mine Metric tons/year

North Antelope 6.78 � 107

Rochelle

Black Thunder 6.13 � 107

which are

Do not writein this book.

http://gpscience.com/chapter_review

Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.

Use the graph below to answer questions 1 and 2.

1. The graph above shows the percentage ofelectricity generated in the United Statesthat comes from various energy sources.According to the graph, about what per-centage comes from fossil fuels?A. 51% C. 65%B. 55% D. 69%

2. The graph shows that approximately whatpercentage of electricity comes from nonre-newable energy sources?A. 97% C. 69%B. 89% D. 55%

3. Which of the following is a typical efficiencyfor a solar cell?A. 10% C. 75%B. 50% D. 95%

4. Which of the following best describes windmills used for the production of electricity?A. They are quiet.B. They can be used anywhere.C. They are 90 percent efficient.D. They are nonpolluting.

5. Which of the following forms only fromancient plant material, not from ancientanimal remains?A. coal C. natural gasB. crude oil D. petroleum

Use the table below to answer questions 6 and 7.

6. The table above shows the efficiency ofdifferent steps in the conversion of fossil fuelsto electricity at a power plant. According tothe table, what is the efficiency for convertingchemical energy in the fossil fuels to heat,and then converting water to steam? A. 30% C. 75%B. 54% D. 90%

7. What is the overall efficiency shown in thetable for converting chemical energy infossil fuels to electricity?A. 35% C. 90%B. 82% D. 95%

Nuclear power20%

Coal51%

Hydroelectric8%

Natural gas14%

Petroleum4%

Sources of Electricity

Other3%

284 STANDARDIZED TEST PRACTICE

Efficiency of Fossil Fuel Conversion

Process Efficiency (%)

Chemical to thermal energy 60

Conversion of water to steam 90

Steam spins turbine 75

Turbine spins electric generator 95

Transmission through power lines 90

Determine the Information Needed Concentrate on whatthe question is asking about a table, instead of all theinformation in the table.

Question 7 Read the question carefully to determine whichrows in the table contain the information needed to answerthe question.

STANDARDIZED TEST PRACTICE 285gpscience.com/standardized_test

Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.

8. Explain why hydroelectric power plantsare almost twice as efficient as fossil fuelor nuclear power plants.

9. About 90 percent of the coal that isused in the United States is used forwhat purpose?

10. What is the most inefficient stage in theproduction of electrical energy at a fossil-fuel burning power plant?

11. Describe the typical disposal method forlow-level nuclear wastes.

Use the illustration below to answer questions 12and 13.

12. The core of a nuclear reactor might con-tain hundreds of fuel rods. Describe thecomposition of a fuel rod.

13. Describe the purpose of the control rodsand explain how their placement in thereactor affects the nuclear chain reaction.

14. Fusion is the most concentrated energysource known. Why, then, is it not used atnuclear plants to make electricity?

Record your answers on a sheet of paper.

Use the photograph below to answer questions 15and 16.

15. The photograph above shows a nuclearpower plant that generates electricityusing the energy released in nuclear fissionof uranium-235. Draw a sketch showingthis fission process. Describe your sketchand explain how the process results in achain reaction.

16. Explain how a nuclear reactor at a nuclearpower plant produces electricity. What isthe purpose of the large tower shown inthe photograph?

17. Explain how the steam that is used to runturbines is produced at a geothermalpower plant.

18. Describe two advantages and three disad-vantages of using solar energy to generateelectricity.

19. Explain why biomass is considered arenewable energy source.

20. Describe the processes that form oil, natu-ral gas, and coal.

21. What is the difference between low-leveland high-level nuclear waste? Describe anexample of each type.

Concreteshield

Steelvessel

Coolingwater

Heatedwater

Reactor core

Controlrods

Fuelrod

bundles

Robert Essel/The Stock Market/CORBIS

http://gpscience.com/standardized_test

chapter 9: energy sources -...

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