Lecture Template 4

7/29/2019 Lecture Template 4

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Hydrocarbons & Allotropes of

Carbon

CHEM 357 Lecture 4

2.1-2.8 & pages 102-103, 105 & 138-139.


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Hydrocarbons

AromaticAliphatic

Alkanes AlkynesAlkenes

Classes of Hydrocarbons


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A straight chain hydrocarbon has the

molecular formula C4H6how many double ()bonds does it contain?

A 0 B 1 C 2 D 3 E 4 FNeed More

Information

Draw potential structures that fit this molecularformula


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Methane (CH4) CH4

Ethane (C2H6) CH3CH3

Propane (C3H8) CH3CH2CH3

bp -160C bp -89C bp -42C

Introduction to Alkanes:Methane, Ethane, and Propane

CnH2n+2


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n-Butane CH3CH2CH2CH3

Isobutane (CH3)3CH

bp -0.4C bp -10.2C

Isomeric Alkanes: The Butanes


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CH3CH2CH2CH2CH2CH3

n-Pentane (BP 36.1C)

n-Hexane (BP 68-69C)

CH3CH2CH2CH2CH3

CH3CH2CH2CH2CH2CH2CH3

n-Heptane (BP 98C)

Higher n-Alkanes


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How Many Isomers?

The number of isomeric alkanes increases as

the number of carbons increase


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Number of ConstitutionallyIsomeric Alkanes

CH4 1

C2H6 1

C3H8 1

C4H10 2

C5H12 3

C6H14 5

C7H16 9

C8H18 18

C9H20 35

C10H22 75

C15H32 4,347

C20H42 366,319

C40H82 62,491,178,805,831


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Physical Properties of Alkanesand Cycloalkanes

A___________is a change in the form ofmatter but not in its chemical identity

A___________occurs whenevercompounds are formed or decomposed

e.g.

Change of Phase (solid/liquid/gas)

Solvation/dissolution


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Boiling Point

Need to overcome inter-molecular forces

(non-covalent interactions)

Governed by strength of intermolecularattractive forces

Alkanes are nonpolar, so dipole-dipole and

dipole-induced dipole forces are absentOnly forces of intermolecular attraction are

_____________________forces.


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Explain how an induced dipole-induceddipole arises


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http://science.howstuffworks.com/environmental/energy/oil-refining5.htm

Sources of Alkanes and Cycloalkanes

25-95 C

70-200 C

100-150 C

150-230 C

200-300 C

300-400 C

350-450 C

400-500+ C

http://www.gcsescience.com/o5.htm

Fractional distillation of crude oil, Fractional tower


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Gasoline is the most valuable fraction of crude

oil refining, however only constitutes ~25% of

the crude oil. Why higher boiling point fractions are

cracked into lower boiling point fractions.

Why lower boiling point fractions arereformed to make higher mw hydrocarbons.


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Cracking

converts high molecular weight hydrocarbons

to more useful, low molecular weight ones

Types of Cracking:

-Thermal Cracking (750-900C, 700 kPa)

-makes ethane & propane-Catalytic Cracking (no O2, 500C & Zeolite)

-makes 3-8 Carbons (propane to octane)

-Hydrocracking (5000 kPa, H2 and Pt catalyst)

-makes Kerosene & gasoline-Thermal Steam Cracking (850C, no O2)

-makes alkenes for plastics & aromatics

-higher temps means more unsaturated HCs

Converting other fractions to gasoline


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Reforming

increases branching of hydrocarbon chainsbranched hydrocarbons have better burning

characteristics for automobile engines

Why do branched hydrocarbons burn better?

Petroleum Refining

More highly branched structures burn smoothly,while unbranched hydrocarbons tend to explode

causing the drive piston forward violently,

creating knocks.


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Octane number

Scale to set up to evaluate burning of gasoline

Gas at the pump is 87, 87% isooctane & 13%heptane

What does unleaded mean?

Aromatics also have high octane ratings

Octane number 100Octane number 0


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Explain how chain length and the degree ofbranching in alkanes have an affect onboiling point

..


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Heptane

bp 98C

Octane

bp 125C

Nonane

bp 150C

Boiling Points


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Octane: bp 125C

2-Methylheptane: bp 118C

2,2,3,3-Tetramethylbutane: bp 107C

Boiling Points


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The Power of

Van der WaalsInteractions


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Gecko foot

A toe of gecko

foot contains

hundreds of

thousands ofsetae and each

seta contains

hundreds ofspatulae

http://academic.udayton.edu/NIRT/gecko.htm


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Using Physical Change as a

Power Source


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Using Physical Change as aPower Source

http://straction.wordpress.com/how-the-steam-engine-of-the-locomotive-works/


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Using Physical Change as aPower Source

http://straction.wordpress.com/how-the-steam-engine-of-the-locomotive-works/


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Why Choose Water ?

Burn Fuel

Heat Liquid Water

Expand to Gas Phase (i.e. Steam)

Push a piston


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Physical Properties of Molecules

The physical properties of a molecule are

encoded by the chemical properties

E.g. melting point, boiling point, solubility


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What Properties are Important inDetermining Boiling Point ?

Already seen hydrocarbons:

28C36C

Hexane Pentane 2-Methylbutane

69C


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Boiling Points

31C 80C 99C

OH

141C

OH

OO

28C


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Boiling Points

31C 80C 99C

OH

141C

OH

OO

28C


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Allotropes of Carbon

Carbon atoms form strong bonds with itself.

C

Bucky ball

Carbon nanotubes

graphite

diamond

31


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Graphene

A single layer of graphite

Atomic scale chicken wire A single layer was first

isolated by using tape to

pull off thinner and

thinner layers

Tape was then dissolved in

acetone.

Done 2004, noble prize2010.


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Applications . . .

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