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290 CHAPTER 10 Energy Sources
Fossil FuelsS E C T I O N
Using EnergyHow many different ways have you used energy today?
You can see energy being used in many ways, throughout theday, such as those shown in Figure 1. Furnaces and stoves usethermal energy to heat buildings and cook food. Air condition-ers use electrical energy to move thermal energy outdoors. Carsand other vehicles use mechanical energy to carry people andmaterials 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. Forexample, energy is used when the chemical energy in fuels istransformed into thermal energy that is used to heat your home.
Sometimes energy is transformed into a form that isn’t use-ful. For example, when an electric current flows through powerlines, about 10 percent of the electrical energy is changed tothermal energy. This reduces the amount of useful electricalenergy that is delivered to homes, schools, and businesses.
� Discuss properties and uses of thethree main types of fossil fuels.
� Explain how fossil fuels areformed.
� Describe how the chemical energyin fossil fuels is converted intoelectrical energy.
Vocabularyfossil fuelspetroleumnonrenewable resource
Fossil fuels are widely used to gener-ate electricity.
Figure 1Energy is used in many ways.
A steel plant uses energy tomake steel products.
Power lines like thesecarry the electrical energyyou use every day.
Automobiles burn gasolineto provide energy.
Energy Use in the UnitedStates More energy is used inthe United States than in anyother country in the world.Figure 2A shows how energy isused in the United States. About20 percent of the energy is usedin homes for heating and cooling,to run appliances, and to providelighting and hot water. About 27percent is used for transportationto power vehicles such as cars,trucks, and aircraft. Another 16percent is used by businesses to heat, cool, and light stores, shops,and office buildings. Finally, about 37 percent of this energy isused by industry and agriculture to manufacture products andproduce food. Figure 2B shows the main sources of the energyused in the United States. Almost 85 percent of the energy usedin the United States comes from burning petroleum, natural gas,and coal. Nuclear power plants provide about eight percent ofthe 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 atoms com-bine with oxygen molecules in the air to form car-bon dioxide and water molecules. This processconverts the chemical energy that is stored in thechemical bonds between atoms to heat and light.Compared to other fuels such as wood, the chemicalenergy that is stored in fossil fuels is more concen-trated. For example, burning 1kg of coal releasestwo to three times as much energy as burning 1 kgof wood. Figure 3 shows the amount of energy thatis produced by burning different fossil fuels.
Woo
d
Coal
Gaso
line
Nat
ural
gas
Ener
gyco
nten
tper
gram
(joul
es)
12,000
36,000
24,000
48,000
Energy Content of Fuels
Figure 3The bar graph shows the amountof energy released by burningone gram of four different fuels.
Residential20%
Industrial37%
Business16%
Transportation27%
Petroleum39%
Coal23%
Natural gas23%
Biomass and other 3%
Hydroelectric 4%
Nuclear8%
Energy Usage Sources of Energy
Figure 2This circle graph shows the
percentages of energy in theUnited States used by homes,businesses, transportation andindustry. This circle graphshows the sources of the energyused in the United States.
SECTION 1 Fossil Fuels 291
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
292 CHAPTER 10 Energy Sources
Petroleum Millions 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 they contain only carbon andhydrogen.
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 andare collected. 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 productsobtained from petroleum are burned to produce energy. About15 percent of the petroleum-based substances that are used inthe United States go toward nonfuel uses. Look around at thematerials in your home or classroom. Do you see any plastics?In addition to fuels, plastics and synthetic fabrics are made fromthe hydrocarbons found in crudepetroleum. Also, lubricants such asgrease and motor oil, as well as theasphalt used in surfacing roads, areobtained from petroleum. Somesynthetic materials produced frompetroleum are shown in Figure 5.
SECTION 1 Fossil Fuels 293
Figure 5The objects shown here are made fromchemical compounds found in petroleum.
Designing an EfficientWater HeaterProcedure1. Measure and record the
mass of a candle.2. Measure 50 mL of water
into a beaker. Record thetemperature of the water.
3. Use the lighted candle toincrease the temperature ofthe water by 10°C. Put outthe candle and measure itsmass 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 to heathot-water tanks. Whatmust be considered in thedesign of these heaters?
Boiler
Steam
WaterFuel
Natural GasThe chemical processes that produce petroleum as ancient
organisms decay also produce gaseous compounds called natu-ral gas. These compounds rise to the top of the petroleumdeposit and are trapped there. Natural gas is composed mostlyof methane, CH4, but it also contains other hydrocarbon gasessuch as propane, C3H8, and butane, C4H10. Natural gas isburned to provide energy for cooking, heating, and manufactur-ing. About one fourth of the energy consumed in the UnitedStates comes from burning natural gas. There’s a good chancethat your home has a stove, furnace, hot-water heater, or clothesdrier 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 under-
ground, such as the one shown in Figure 6. In the first half ofthe twentieth century, most houses in the United States wereheated by burning coal. In fact, during this time, coal providedmore than half of the energy that is used in the United States.Now almost two thirds of the energy used comes from petro-leum and natural gas, and only about one fourth comes fromcoal. About 90 percent of all the coal that is used in the UnitedStates is burned by power plants to generate electricity.
294
Figure 6Coal mines usually are locateddeep underground.
Stage 1 The chemical energy in the fossil fuel is converted to thermal energy as the fuel is burned in the boiler. Only about 60 percent of the available chemical energy is converted into thermal energy.
Stage 2 The thermal
Stage 2 The thermal energy heats water and produces steam. This stage is 90 percent efficient.
Nuclear power20%
Coal51%
Hydroelectric8%
Natural gas14%
Petroleum4%
Sources of Electricity
Other3%
Origin of Coal Coal mines were once the site ofancient swamps where large, fernlike plants grew.Coal formed from this plant material. Worldwide,the amount of coal that is potentially available isestimated to be 20 to 40 times greater than the sup-ply of petroleum.
Coal also is a complex mixture of hydrocarbonsand other chemical compounds. Compared topetroleum and natural gas, coal contains moreimpurities, such as sulfur. As a result, more pollu-tants, such as sulfur dioxide, are produced when coalis burned.
Generating Electricity Figure 7 shows that almost 70 percent of the elec-
trical energy used in the United States is produced byburning fossil fuels. How is the chemical energy contained in fos-sil fuels converted 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, theelectric current is transmitted to homes, schools, and businessesthrough power lines.
Turbine Transformer
Power lines
Intake pipe
Generator
Figure 8Fossil fuels are burned to gener-ate electricity in a power plant.
295
Figure 7This circle graph shows the per-centage of electricity generatedin the United States that comesfrom various energy sources.
Stage 3 The steam at high pressure strikes the blades of a turbine and causes it to spin. This stage is 75 percent efficient.
Stage 4 The rotating turbine spins an electric generator. Ninety-five percent of the mechanical energy in the rotating turbine is converted into electrical energy.
Stage 5 Electrical current is transmitted along power lines. Electrical resistance converts some of the electrical energy to thermal energy. This stage is 90 percent efficient.
Efficiency of PowerPlants
When fossil fuels are burned toproduce electricity, not all the chemi-cal energy in the fuel is converted toelectrical energy. Energy is lost inevery stage of the process. No stage is100 percent efficient.
The overall efficiency of theentire process is given by multiplyingthe efficiencies of each stage of theprocess shown in Table 1. If you wereto do this, you’d find that the result-ing overall efficiency is only about 35
percent. This means that only about 35 percent of the energycontained in the fossil fuels is delivered to homes, schools, andbusinesses as electrical energy. The other 65 percent is lost as thechemical energy in the fuel is transformed into electrical energyand delivered to energy users.
The Costs of Using Fossil FuelsAlthough fossil fuels are a useful source of energy for generat-
ing electricity and providing the power for transportation, theiruse has some undesirable side effects. When petroleum productsand coal are burned, smoke is given off that contains small parti-cles called particulates. These particulates cause breathing prob-lems for some people. Burning fossil fuels also releases carbondioxide. Figure 9 shows how the carbon dioxide concentration inthe atmosphere has increased from 1960 to 1999. The increasedconcentration of carbon dioxide in the atmosphere might causeEarth’s surface temperature to increase.
Using Coal The most abundant fossil fuel iscoal, but coal contains even more impuritiesthan oil or natural gas. Many electric powerplants that burn coal remove some of thesepollutants before they are released into theatmosphere. Removing sulfur dioxide, forexample, helps to prevent the formation ofcompounds that might cause acid rain. Miningcoal also can be dangerous. Miners risk beingkilled or injured, and some suffer from lungdiseases caused by breathing coal dust overlong periods of time.
296 CHAPTER 10 Energy Sources
1995199019851980197519701965300
325
350
375
Year
CO Concentration from 1960 to 19992
CO c
once
ntra
tion
(par
ts p
er m
illio
n)2
Figure 9The carbon dioxide concentrationin Earth’s atmosphere has beenmeasured at Mauna Loa inHawaii. From 1960 to 1999, thecarbon dioxide concentration has increased by about 16percent.
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
Nonrenewable ResourcesIt’s a safe bet that almost any time you use
an electrical appliance or ride in a car, sometype of fossil fuel is the energy source that isbeing used. All fossil fuels are nonrenewableresources, which means they are resources thatcannot be replaced by natural processes asquickly as they are used. Therefore, fossil fuelreserves are decreasing as population and indus-trial demands are increasing. Figure 10 showshow the production of oil might decline overthe next 50 years as oil reserves are used up. Asthe production of energy from fossil fuels con-tinues, the remaining reserves of fuel will decrease. Fossil fuelswill become more difficult 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. To meet these energy demands,the use of fossil fuels must be reduced and energy must beobtained from other sources. One way to reduce the use of fossilfuels is to make vehicles that are more fuel efficient. You canhelp reduce the demand for energy by not wasting energy inyour daily activities.
Why is it important to conserve nonrenewableresources?
SECTION 1 Fossil Fuels 297
Section Assessment
1. Describe the three main forms of fossil fuels.
2. What are the advantages and disadvan-tages of using coal to generate electricity?
3. How are the different chemicals in crude oilseparated?
4. Give three examples of different productsderived from chemicals in crude oil.
5. Think Critically If fossil fuels are stillforming, why are they considered to benonrenewable resources?
6. Comparing and Contrasting Compare andcontrast the different fossil fuels. Include theadvantages and disadvantages of using each asa source of energy. For more help, refer to theScience Skill Handbook.
7. Communicating In your Science Journal,make a list of areas in your school where energyuse could be reduced. For more help, refer tothe Science Skill Handbook.
2050203020101990197019501930Year
Global Oil Production
5
10
15
20
25
30
0
Oil
prod
uctio
n(b
illio
nsof
barr
els)
Figure 10Some predictions show thatworldwide oil productionwill peak by 2005 and thendecline rapidly over the following 50 years.