Sandstone Shale Limestone. Water. Section Resources

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1 FOCUS Objectives Identify three important fossil fuels and describe their origins Describe the composition of natural gas, petroleum, and coal Describe What happens when petroleum is refined. Guide for Reading Build Vocabulary Word Forms Relate the chemical process of cracking to the physical process when an objects cracks or breaks apart. Reading Strategy Relating Text and Visuals Have students relate the description of fractions in Table 22.4 to the diagram of the fractionating column in Figure INSTRUCT Have students read the introduction. Then ask, Why are hydrocarbons harder to obtain on Earth than they would be on Titan? (On Earth, the hydrocarbons are in the crust, not in the atmosphere.) Natural Gas Relate It was not until the invention of the kerosene lamp that people valued petroleum. By the time electric lights reduced the need for kerosene, automobiles required gasoline, which previously had been discarded as a useless by-product of kerosene production. Before the petroleum era began, fats from domesticated animals, whale oil, wood, and coal were used as energy sources Hydrocarbons From Earth s Crust Guide for Reading Key Concepts What type of hydrocarbons are in natural gas? What is the first step in the refining of petroleum? How is coal classified? What is the chemical composition of coal? Vocabulary cracking Reading Strategy Previewing Before you read, jot down five things you know about petroleum. As you read, explain how what you learn relates to what you already know. Natural gas Petroleum 712 Chapter 22 Sandstone Shale Limestone Water Section Resources Print Guided Reading and Study Workbook, Section 22.5 Core Teaching Resources, Section 22.5 Review Transparencies, T260 T261 The photograph shows a painting in which the artist imagines Saturn s moon Titan as a refueling station in space. A traveler would refill a fuel tank with hydrocarbons from Titan s atmosphere. On Earth, hydrocarbons are also used as fuels. However, they are more difficult to obtain because they are found in Earth s crust, not in Earth s atmosphere. In this section, you will learn about three fossil fuels natural gas, petroleum, and coal. Natural Gas Much of the world s energy is supplied by burning fossil fuels. Fossil fuels are carbon-based because they are derived from the decay of organisms. Millions of years ago, marine organisms died, settled on the ocean floor, and were buried in ocean sediments. Heat, pressure, and bacteria changed the residue into petroleum and natural gas, which contain mostly aliphatic hydrocarbons. Figure shows one possible location for these fuels. Natural gas is an important source of alkanes of low molar mass. Typically, natural gas is composed of about 80% methane, 10% ethane, 4% propane, and 2% butane. The remaining 4% consists of nitrogen and hydrocarbons of higher molar mass. Natural gas also contains a small amount of the noble gas helium. In fact, natural gas is a major source of helium. Methane, the major constituent of natural gas, is especially prized for combustion because it burns with a hot, clean flame. CH 4 (g) 2O 2 (g) CO 2 (g) 2H 2 O(g) heat Propane and butane are separated from the other gases in natural gas by liquefaction. These heating fuels are sold in liquid form in pressurized tanks as liquid petroleum gas (LPG). Oxygen is necessary for the efficient combustion of a hydrocarbon. If there is not enough oxygen available, the combustion is incomplete. Complete combustion of a hydrocarbon gives a blue flame. Incomplete combustion gives a yellow flame. This is due to the formation of small, glowing carbon particles that are deposited as soot when they cool. Carbon monoxide, a toxic gas, is also formed along with carbon dioxide and water during incomplete combustion. Figure Wells are drilled to reach natural gas and petroleum. Pressure from the trapped gas may force petroleum up a well pipe, but pumping is usually required. Technology Interactive Textbook with ChemASAP, Assessment 22.5 Go Online, Section Chapter 22

2 Petroleum The organic compounds found in petroleum, or crude oil, are more complex than those in natural gas. Most of the hydrocarbons in petroleum are straight-chain and branched-chain alkanes. Petroleum also contains small amounts of aromatic compounds and sulfur-, oxygen-, and nitrogencontaining organic compounds. Humans have known about petroleum for centuries; ancient peoples found it seeping from the ground in certain areas. In the late 1850s, a vast deposit of petroleum was discovered in Pennsylvania when a well was drilled to obtain petroleum for use as a fuel. Within decades, petroleum deposits had also been found in the Middle East, Europe, and the East Indies. Petroleum has since been found in other parts of the world as well. Petroleum is a mixture of hydrocarbons having from one to more than 40 carbon atoms. Without further treatment, petroleum is not very useful. The mixture must be separated, or refined, into parts called fractions, which have many commercial uses. The refining process starts with the distillation of petroleum (crude oil) into fractions according to boiling point. A schematic of a petroleum refining distillation tower is shown in Figure Each distillation fraction contains several different hydrocarbons. The fractions and their composition are listed in Table The amounts of products obtained by fractional distillation are not in proportion to the demand of the market. Gasoline is by far the most commonly used product, so other processes are used to make the supply meet the demand. Cracking is a controlled process by which hydrocarbons are broken down or rearranged into smaller, more useful molecules. For example, fractions containing compounds of higher molar mass are cracked to produce the more useful short-chain components of gasoline and kerosene. Hydrocarbons are cracked with the aid of a catalyst and with heat. This process also produces low-molar-mass alkanes, which are used to manufacture paints and plastics. Other catalytic processes besides cracking are used to increase the amounts of components that improve the performance of gasoline. Checkpoint Table 22.4 Fraction When and where was the first petroleum well drilled? Fractions Obtained from Crude Oils Composition of carbon chains Boiling range ( C) Percent of crude oil Natural gas C 1 to C 4 Below 20 Petroleum ether (solvent) C 5 to C 6 30 to 60 s 10% Naphtha (solvent) C 7 to C 8 60 to 90 Gasoline C 5 to C to % Kerosene C 12 to C to % Fuel oils, mineral oil C 15 to C to % Lubricating oil, petroleum jelly greases, paraffin wax, asphalt C 16 to C 24 Over % Fractionating Column Gasoline vapors Condenser Gas Gasoline 40 o C 175 o C Kerosene 150 o C 275 o C Fuel oil 225 o C 400 o C Lubricating oil over 400 o C Crude oil vapors from heater Steam Residue (wax, asphalt, tar) Figure In fractional distillation, the crude oil is heated so that it vaporizes and rises through the fractionating column. The column is hotter at the bottom and cooler at the top. Compounds with the highest boiling points condense near the bottom. Compounds with the lowest boiling points condense near the top. Petroleum Discuss Review the balanced equation for combustion of methane and explain the conditions that lead to the formation of CO. Refer students to Carbon Monoxide on page R23 of the Elements Handbook. CLASS Activity Fractions of Crude Oil Divide the class into five groups. Have each group create a display on one of the fractions obtained from crude oil. Each group should use Table 22.4 to make a pie graph of the percents of the fractions in crude oil, highlighting the slice that represents their fraction. Displays should also include information on the composition of the fraction and uses of the products derived from that fraction. Students can illustrate their displays with original art or magazine photographs. Section 22.5 Hydrocarbons From Earth s Crust 713 Differentiated Instruction Gifted and Talented L3 Have students research the energy sources used in the United States. Have them summarize their findings in a bar chart showing to what extent the United States depends on each type of energy source. The bar chart should profile the energy sources for the years 1850, 1900, 1950, 1990, and Gifted and Talented L3 Have students research one or more specific examples in which bacteria have been used to clean up an oil spill. Was the method successful? Why or why not? Challenge the students to explain how such organisms are able to metabolize hydrocarbons. What are the products of the bacterial digestion of oil? Answers to... Checkpoint in the late 1850s In Pennsylvania Hydrocarbon Compounds 713

3 Section 22.5 (continued) Coal Discuss Have students study Figure and read the caption. If possible, show the students samples of peat, lignite, bituminous coal, and anthracite coal. Explain that coal can be converted to methane by a process called coal gasification in which coal and hydrogen react under high temperature and pressure. Synthetic crude oil can be made by a process called coal liquefaction in which coal is dissolved in a solvent at high pressure and temperature. The product, called solvent-refined coal, is then purified and heated. The hard, brittle residue that remains can be melted and used as a liquid fuel. For: Links on Natural Resources Visit: Web Code: cdn-1225 Figure Coal formed when tree ferns and mosses died. The layers of decaying organic material were compressed over millions of years between layers of soil and rock. The first stage in coal formation is peat. Continued pressure and heat transform peat into lignite, bituminous coal, and anthracite coal. Coal Geologists think that coal had its origin some 300 million years ago when huge tree ferns and mosses grew abundantly in swampy tropical regions. When the plants died, they formed thick layers of decaying vegetation. Layer after layer of soil and rock eventually covered the decaying vegetation, which caused a buildup of intense pressure. This pressure, together with heat from Earth s interior, slowly turned the plant remains into coal. Coal Formation The first stage in the formation of coal is an intermediate material known as peat. Peat, shown in Figure 22.15, is a soft, brown, spongy, fibrous material. When first dug out of a bog, peat has a very high water content. After it has been allowed to dry, it produces a low-cost but smoky fuel. If peat is left in the ground, it continues to change. After a long period of time, peat loses most of its fibrous texture and becomes lignite, or brown coal. Lignite is much harder than peat and has a higher carbon content (about 50%). The water content, however, is still high. Continued pressure and heat slowly change lignite into bituminous, or soft coal. Bituminous coal has a lower water content and higher carbon content (70 80%) than lignite. In some regions of Earth s crust, even greater pressures have been exerted. In those places, such as eastern Pennsylvania, soft coal has been changed into anthracite, or hard coal. Anthracite has a carbon content that exceeds 80%, making it an excellent fuel source. Coal is classified by its hardness and carbon content. Coal, which is usually found in seams from 1 to 3 meters thick, is obtained from both underground and surface mines. In North America, coal mines are usually less than 100 meters underground. Much of the coal is so close to the surface that it is strip-mined, as shown in Figure By contrast, many coal mines in Europe and other parts of the world extend 1000 to 1500 meters below Earth s surface. Download a worksheet on Natural Resources for students to complete, and find additional teacher support from NSTA SciLinks. Peat Bituminous Lignite Anthracite 714 Chapter 22 Facts and Figures Cleaning up Oil Spilled oil from oil tankers can destroy fragile marine ecosystems. Because cleaning up oil spills is difficult and expensive, researchers are developing new cleanup technologies and safer transportation methods. Most current cleanup methods involve containing the oil and either pumping it away or soaking it up with absorbent materials. Some of the new developments include the genetic engineering of bacteria to eat up the oil spill and the design of double-hulled tankers that are less likely to spill their oil in a collision. 714 Chapter 22

4 Composition of Coal Coal consists largely of condensed aromatic compounds of extremely high molar mass. These compounds have a high proportion of carbon compared with hydrogen. Due to the high proportion of aromatic compounds, coal leaves more soot upon burning than do the more aliphatic fuels obtained from petroleum. The majority of the coal that was once burned in North America contained about 7% sulfur, which burns to form the major air pollutants SO 2 and SO 3. Coal may be distilled to obtain a variety of products: coke, coal tar, coal gas, and ammonia. Coke is the solid material left after coal distillation. It is used as a fuel in many industrial processes and is the crucial reducing agent in the smelting of iron ore. Because it is almost pure carbon, coke produces intense heat and little or no smoke when it burns. Coal gas consists mainly of hydrogen, methane, and carbon monoxide, all of which are flammable. Coal tar can be distilled further into benzene, toluene, naphthalene, phenol, and pitch. The ammonia from distilled coal is converted to ammonium sulfate for use as a fertilizer Section Assessment 30. Key Concept Describe the hydrocarbons found in natural gas. 31. Key Concept Describe the first process used in the refining of petroleum. 32. What are the two variables used to classify coal? 33. Key Concept Describe the chemical composition of coal. 34. How did the three major fossil fuels form? 35. What are the principal sources of aliphatic hydrocarbons? What is the principal source of aromatic hydrocarbons? 36. Explain why cracking is a necessary step in petroleum refining. 30. alkanes of low molar mass 31. The refining process starts with the distillation of petroleum into fractions according to boiling point. 32. hardness and carbon content 33. Coal consists largely of condensed ring compounds of extremely high molar mass. These compounds have a high ratio of carbon to hydrogen. Section 22.5 Assessment Handbook Catalytic Converters When fossil fuels burn in an internal combustion engine, the exhaust contains more than carbon dioxide gas and water vapor. Read about catalytic converters on R42. Write a paragraph explaining what happens to pollutants in a catalytic converter. Assessment 22.5 Test yourself on the concepts in Section withchemasap Figure Coal is mined from both surface mines, shown here, and underground mines. Section 22.5 Hydrocarbons From Earth s Crust Heat, pressure, and bacteria changed marine organisms buried in ocean sediments into petroleum and natural gas. Heat and pressure changed buried layers of vegetation into coal. 35. natural gas and petroleum, coal 36. Amounts of products obtained by fractional distillation don t match demands. Cracking breaks down hydrocarbons into smaller, more useful components. 3 ASSESS Evaluate Understanding Have students compare the formation of coal, natural gas, and petroleum. (Petroleum and natural gas are derived from marine organisms buried under ocean sediments; coal, from buried wetland plants. Natural gas and petroleum contain mostly aliphatic compounds; coal contains a large percentage of aromatic compounds.) Reteach L1 Display Figure on an overhead projector. If possible, bring a sample of crude oil to class so that students can observe its color and odor. Explain that petroleum is a complex mixture of hydrocarbons whose molecules range in size from 5 to 30 carbon atoms. To be used effectively, the crude oil must be refined by fractional distillation, which separates compounds on the basis of their boiling points. Explain that in general, low molar mass compounds have low boiling points and high molar mass compounds have high boiling points. Elements Handbook Transition metals, such as rhodium and platinum, act as catalysts for reactions that change nitrogen oxides to nitrogen, and hydro carbons and carbon monoxide to carbon dioxide and water. If your class subscribes to the Interactive Textbook, use it to review key concepts in Section with ChemASAP Hydrocarbon Compounds 715

5 A Number You Can t Knock Causes of Knocking Knocking is influenced by two main variables. The first variable is engine compression the degree to which the gas air mixture in the cylinder is compressed prior to ignition by the spark plug (see Step 2). The higher the compression, the more power delivered by the ignition of the fuel. Higher compression also means greater likelihood of engine knock. The second variable is the chemical structure of the hydrocarbons that make up the fuel. Straight-chain alkanes are more prone to knocking than are branched-chain alkanes, cycloalkanes, and aromatic hydrocarbons. In practice, these two variables mean that engine compression and thus performance is limited by the composition of the gasoline used. Octane Ratings The designers of the octane system developed a way of testing fuels in a special one-cylinder engine with a variable compression ratio. For each fuel tested, they could increase the compression until the engine began to knock. Then they chose two pure fuels as standards against which to measure others heptane and isooctane (2,2,4-trimethylpentane). These two hydrocarbons had similar physical properties, but isooctane was very resistant to knocking, and heptane was very prone to it. The designers arbitrarily assigned heptane an octane rating of 0 and isooctane a rating of 100. Every fuel tested could then be assigned an octane number relative to these hydrocarbons. An octane rating of 89 meant that fuel performed the same in the special test engine as a mixture that was 89 parts isooctane and 11 parts heptane. A Number You Can t Knock Engine knock is the sound an engine makes when gasoline ignites too soon, possibly because of poor engine timing or the use of low octane fuel. Knocking can cause overheating, loss of power, and engine damage. A gasoline s octane rating is a measure of its ability to resist engine knock. Applying Concepts What happens to the pressure inside the cylinder during Step 2. 1 Intake Gasoline and air are mixed in a cylinder of an internal combustion engine. 716 Chapter 22 2 Compression The gas air mixture is compressed. The greater the compression, the greater the engine s power, and the more likely the engine is to knock. Octane Ratings Octane ratings are based on isooctane, which resists engine knock, and heptane, which is prone to engine knock. Isooctane has a rating of 0. Heptane has a rating of 100. So an octane rating of 89 means that the gasoline blend performs as though it were 89 parts isooctane and 11 parts heptane. Engine knock Knocking occurs when the fuel ignites by itself in the engine cylinder. Often this ignition occurs prior to spark ignition. The sound comes from the vibration of the piston, connecting rod, and bearings. 716 Chapter 22

6 Oil refineries To make gasoline, a refinery separates crude oil into various components. Refinery technicians combine some of the components, performance additives, and dyes to make different grades of fuel. This fuel rating system is still in use today. The major modification is that two somewhat different testing methods are used. One, called the motor octane rating (M), tests the fuel under conditions that approximate highspeed driving with heavy loads. The other, called the research octane rating (R), uses conditions that simulate more normal driving. Usually, the octane number assigned to gasolines is an average of the numbers given by these two methods. This is indicated on gasoline pumps as (R + M) / 2. Discuss Review the refining processes used to convert large molar mass hydrocarbons to smaller branched-chain hydrocarbons. Point out that the petroleum industry uses cracking, reforming, and isomerization to produce gasolines with the desired octane rating. Cracking is the process by which large hydrocarbons are broken down into smaller molecules with a catalyst and heat. Reforming and isomerization are the processes used to convert straight-chain alkanes, such as n-octane, to branched-chain alkanes, such as isooctane. 3 Combustion A spark plug ignites the compressed mixture. The combustion products push down a cylinder that turns the crankshaft. 4 Exhaust The cylinder clears the chamber of combustion products, such as carbon dioxide. Technology and Society 717 Answers to... Applying Concepts The pressure inside the cylinder increases during Step 2. Hydrocarbon Compounds 717