22.5 hydrocarbons from earth’s crust 1 > copyright © pearson education, inc., or its...

22.5 Hydrocarbons From 22.5 Hydrocarbons From Earth’s CrustEarth’s Crust

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Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Chapter 22Hydrocarbon Compounds

22.1 Hydrocarbons22.2 Unsaturated Hydrocarbons22.3 Isomers22.4 Hydrocarbon Rings

22.5 Hydrocarbons From Earth’s Crust


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Where does gasoline come from?

CHEMISTRY & YOUCHEMISTRY & YOU

You might think it comes from the gas station, but what about before that? In this lesson, you’ll find out where gasoline comes from and how it is refined.


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Natural Gas

• What hydrocarbons are in natural gas?

Natural GasNatural Gas


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The burning of fossil fuels produces much of the world’s energy.


• 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.


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This figure shows how natural gas is often found overlaying oil deposits or in separate pockets in rock.



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• Natural gas is an important source of alkanes of low molar mass.

• Typically, natural gas is composed of about 80 percent methane, 10 percent ethane, 4 percent propane, and 2 percent butane.

• The remaining 4 percent 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.


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Methane, the major constituent of natural gas, is especially prized for combustion because it burns with a hot, clean flame.


CH4(g) + 2O2(g) → CO2(g) + 2 H2O(g) + heat


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• 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).



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Oxygen is necessary for the efficient combustion of a hydrocarbon. If there is not enough oxygen available, the combustion is incomplete.


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• Complete combustion of a hydrocarbon produces a blue flame.




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• Complete combustion of a hydrocarbon produces a blue flame.

• Incomplete combustion produces a yellow flame.– The yellow color is due to the formation of small,

glowing carbon particles that are deposited as soot when they cool.

– Carbon monoxide, a toxic gas, also forms along with carbon dioxide and water during incomplete combustion.




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What is the major component of natural gas?


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What is the major component of natural gas?

Methane; natural gas is composed of about 80 percent methane.


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Petroleum

• What is the first step in the refining of petroleum?

PetroleumPetroleum


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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.

• But petroleum also contains small amounts of aromatic compounds and sulfur-, oxygen-, and nitrogen-containing organic compounds.

PetroleumPetroleum


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• In the 1850s, a vast deposit of petroleum was discovered in Pennsylvania.

• 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.

PetroleumPetroleum

Humans have known about petroleum for centuries; ancient peoples found it seeping from the ground in certain areas.


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• Crude oil is a mixture of hydrocarbons having anywhere from 1 carbon atom to more than 40 carbon atoms.

• The mixture must be separated, or refined, into parts called fractions, which have many commercial uses.

• Petroleum refining begins with the distillation of crude oil into fractions according to boiling point.

PetroleumPetroleum


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This figure shows a schematic of a petroleum reining distillation tower. Each distillation fraction contains several different hydrocarbons.

PetroleumPetroleum


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PetroleumPetroleum

Note that the gasoline fraction makes up just 40 percent of the crude oil mixture.

• However gasoline is by far the most commonly used petroleum product.

• To make the supply meet the demand, other processes such as cracking are used.


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PetroleumPetroleum

Cracking is a controlled process by which hydrocarbons are broken down or rearranged into smaller, more useful molecules.


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• For example, fractions containing compounds of higher molar mass are “cracked” to produce the more useful short-chain components of gasoline and kerosene.

• This process also produces low-molar-mass alkanes, which are used to manufacture paints and plastics.

PetroleumPetroleum

Cracking is a controlled process by which hydrocarbons are broken down or rearranged into smaller, more useful molecules.


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When crude oil is refined, what percentage of the crude oil mixture does the gasoline fraction make up?


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When crude oil is refined, what percentage of the crude oil mixture does the gasoline fraction make up?

The gasoline fraction makes up 40 percent of the crude oil mixture.


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Coal

• What characteristics are used to classify coal?

CoalCoal


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CoalCoal

Geologists think that coal had its origin some 300 million years ago when huge tree ferns and mosses grew abundantly in swampy tropical regions.


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• When the plants died, they formed thick layers of decaying vegetation.

CoalCoal



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• Layer after layer of soil and rock eventually covered the decaying vegetation, which caused a buildup of intense pressure.

CoalCoal



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• 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.

CoalCoal



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CoalCoal

Coal Formation

The first stage in the formation of coal is an intermediate, wet, fibrous material known as peat.• After it has been

allowed to dry, it produces a low-cost but smoky fuel.


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CoalCoal

Coal Formation

If the 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.


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CoalCoal

Continued pressure and heat transform peat into lignite, bituminous coal, and anthracite coal.


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CoalCoal

Coal Formation

Coal is classified by its hardness and carbon content.


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CoalCoal

• For example, lignite is much harder than peat and has a higher carbon content (about 30 percent).

Coal Formation



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CoalCoal

• Continued pressure and heat slowly change lignite into bituminous coal, or soft coal, which is harder than lignite.

Coal Formation



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CoalCoal

• In some regions of Earth’s crust, even greater pressures have been exerted. In those places, such as the earth beneath eastern Pennsylvania, soft coal has been changed into anthracite, or hard coal.

Coal Formation



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CoalCoal

• Anthracite has a carbon content that exceeds 85 percent, making it an excellent fuel source.

Coal Formation



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• 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.

• By contrast, many coal mines in Europe and Asia extend 1000 to 1500 meters below Earth’s surface.

CoalCoal

Coal Formation

Coal, which is usually found in seams from 1 to 3 meters thick, is obtained from both underground and surface mines.


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Where does gasoline come from? Where does coal come from?



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Where does gasoline come from? Where does coal come from?


Gasoline is made by the fractional distillation of crude oil. Coal is mined directly from underground sources. Both are derived from decayed organic material.


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• These compounds have a high proportion of carbon compared with hydrogen.

• Due to the high proportion of aromatic compounds, coal leaves more soot when burned than the more aliphatic fuels obtained from petroleum.

CoalCoal

Composition of Coal

Coal consists largely of condensed aromatic compounds of extremely high molar mass.


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• As coal burns, the sulfur oxidizes to form SO2 and SO3, two major air pollutants that contribute to acid rain and smog.

– In order to reduce air pollution, the majority of sulfur is removed before the coal is burned.

CoalCoal

Composition of Coal

Coal also contains a small amount of sulfur.


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CoalCoal

Composition of Coal

Coal may be distilled to obtain a variety of products: coal gas, coal tar, ammonia, and coke.• Coke is the solid material left after coal

distillation.– It is used as a fuel and is the crucial reducing

agent in the smelting of iron ore.


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CoalCoal

Composition of Coal

Coal may be distilled to obtain a variety of products: coal gas, coal tar, ammonia, and coke.• Coal gas consists mainly of hydrogen,

methane, and carbon monoxide.


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CoalCoal

Composition of Coal

Coal may be distilled to obtain a variety of products: coal gas, coal tar, ammonia, and coke.• Coal gas consists mainly of hydrogen,

methane, and carbon monoxide.

• Coal tar can be distilled further into benzene, toluene, naphthalene, phenol, and pitch.


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CoalCoal

Composition of Coal

Coal may be distilled to obtain a variety of products: coal gas, coal tar, ammonia, and coke.• The ammonia from distilled coal is converted

to ammonium sulfate for use as a fertilizer.


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Why does coal produce more soot when burned than fuels derived from petroleum?


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Why does coal produce more soot when burned than fuels derived from petroleum?

Coal produces more soot when burned because it consists largely of condensed aromatic compounds that have high molar masses and high proportions of carbon compared with hydrogen.


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Natural gas is an important source of alkanes of low molar mass.

Petroleum refining begins with the distillation of crude oil into fractions according to boiling point.


Key ConceptsKey Concepts


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• cracking: the controlled process by which hydrocarbons are broken down or rearranged into smaller, more useful molecules

Glossary TermsGlossary Terms


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END OF 22.5END OF 22.5

22.5 hydrocarbons from earth’s crust 1 > copyright © pearson education, inc., or its...

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