2'7 Physical Properties of Alkanes 2'8 Reactions of Alkanes 2'9 Sources of Alkanes

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2.7 Physical Properties of Alkanes2.8 Reactions
of Alkanes2.9 Sources of Alkanes

• Lecture 7

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2.7A Alkane Boiling Points

• C1 - C4 Gas at RT
• C5 - C17 Liquid at RT
• gt C17 Solid at RT

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2.7B Intermolecular Interactions

• Dispersion Forces are weak
• Based on Instantaneous Electron Distribution
• Induced Temporary Dipole
• Leads to Electrostatic Interaction
• Dispersion Forces stronger with larger atoms and
  molecules

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• Higher Molecular Weight means Higher Melting
  Point for Alkanes
• Density for all alkanes 0.7 - 0.8 g/mL
• Alkanes float on water

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Constitutional Isomers

• Have different physical properties
• Isomers have different MPs,BPs, densities
• Less branching leads to more dispersion forces
• C6 Straight Chain alkane has higher BP

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2.8 Reactions of Alkanes

• Generate heat and power from alkanes
• Energy released is Heat of Combustion

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Heat of Combustion and Stability

• Branching Increases Stability
• Ring strain is measured by combustion
• Consider cyclic vs. unbranched

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2.9 Sources and Importance of Alkanes

• Fossil Fuels
• Natural gas, Petroleum and Coal
• Account for 90 of Energy Consumption

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2.9A Natural Gas

• 90-95 Methane, 5-10 Ethane
• Ethylene comes from CRACKING ethane
• CRACKING Convert to Unsaturated
• Cracking requires very high temp 800 ºC

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2.9B Petroleum

• Thick mixture of thousands of compounds
• Hydrocarbons from marine plant and animal
  decomposition
• Used for fuel and lubricants
• Petroleum Natural gas used for 90 of organic
  product manufacturing

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Petroleum Refining

• Produce usable products
• Minimize waste
• Divided into two categories
• SEPARATION
• REFORMING

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Refining

• Fractional Distillation
• Components separated based on BP
• Gasoline
• Lubricating Oil
• Asphalt

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Reforming

• Cracking Ethane ? Ethene
• Catalytic Reforming
• Hexane ? Cyclohexane ? Benzene

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2.9C Coal

• Synthesis gas Mix of CO H2

Uses for Synthesis Gas Making Methanol, Acetic
Acid, etc.