6.3.1 Properties of Alkanes

• The general formula for alkanes is $C_{n}H_{2n + 2}$
• Alkanes have only single bonds between carbon atoms.
• The physical properties of alkanes are primarily influenced by intermolecular forces and molecular size
• Match the property of alkanes with its description:

  Boiling Point ↔️ Increases with chain length

  Solubility ↔️ Insoluble in water

  Density ↔️ Generally increases with chain length
• Why do alkanes have low boiling points?

  Weak London dispersion forces
• Alkanes are hydrophobic because they are nonpolar.
• Alkanes are less dense than water
• Match the alkane with its formula:

  Methane ↔️ $CH_{4}$

  Ethane ↔️ $C_{2}H_{6}$

  Propane ↔️ $C_{3}H_{8}$
• Order the physical properties of alkanes based on how they change with increasing chain length:

  1️⃣ Boiling Point increases

  2️⃣ Melting Point increases

  3️⃣ Solubility decreases

  4️⃣ Density increases
• Longer alkane chains have stronger London dispersion forces due to their increased surface area.
• As chain length increases, alkanes remain insoluble in water but soluble in nonpolar solvents.
• Why does the boiling point of alkanes increase with increasing chain length?

  Stronger London dispersion forces
• Alkanes are insoluble in water but soluble in nonpolar solvents
• What happens to the density of alkanes as chain length increases?

  Generally increases
• Alkanes primarily undergo two main reactions: halogenation and combustion
• In halogenation, a hydrogen atom is replaced with a halogen
• What are the products of combustion of alkanes?

  Carbon dioxide and water
• Steps in the halogenation of methane

  1️⃣ Initiation: UV light breaks $Cl_{2}$ into radicals

  2️⃣ Propagation: A chlorine radical attacks $CH_{4}$

  3️⃣ Termination: Two radicals combine to form a stable molecule
• Is the combustion of alkanes exothermic or endothermic?

  Exothermic
• Complete combustion of alkanes requires excess oxygen
• Incomplete combustion of alkanes produces carbon monoxide, water, and carbon soot
• What is the general formula for alkanes?

  $C_{n}H_{2n + 2}$
• Match the alkane with its formula:

  Methane ↔️ $CH_{4}$

  Ethane ↔️ $C_{2}H_{6}$

  Propane ↔️ $C_{3}H_{8}$
• The density of alkanes generally increases with chain length but remains less than water
• Why does the boiling point of alkanes increase with chain length?

  Stronger London dispersion forces
• What happens to the solubility of alkanes in polar solvents as chain length increases?

  Decreases
• Alkanes undergo halogenation via a free radical mechanism
• Combustion is a reaction with oxygen to produce carbon dioxide and water
• Combustion releases significant energy and is used in fuels
• Why are alkanes generally unreactive?

  Strong C-C and C-H bonds
• In halogenation, hydrogen atoms in alkanes are replaced by halogen atoms.
• Combustion of alkanes is an exothermic reaction
• Steps in the free radical mechanism of alkane halogenation

  1️⃣ Initiation

  2️⃣ Propagation

  3️⃣ Termination
• Steric strain refers to the repulsion between bulky groups within a molecule
• Alkanes are stable due to their strong C-C and C-H single bonds
• Match the alkane with its practical application:

  Methane ↔️ Natural gas fuel

  Propane ↔️ BBQ gas

  Butane ↔️ Lighter fluid

  Hexane ↔️ Solvent in extraction
• What properties of alkanes make them useful in practical applications?

  Boiling points and solubility