Alkanes

• Alkanes


  Saturated hydrocarbons that contain only carbon-carbon and carbon-hydrogen single bonds
• Saturated


  Compounds contain single bonds only
• Hydrocarbons

  Compounds containing carbon and hydrogen only
• Physical properties of alkanes

  • Boiling point increases with increasing carbon chain length
  • Boiling point decreases with increasing number of branches
• Fractional distillation

  1. Crude oil is heated to vaporise it and enters the column

  2. Hydrocarbons have different boiling points

  3. Boiling point depends on size/Mr/chain length

  4. The column is cooler at top and hotter at the bottom

  5. Larger molecules with higher boiling points condense at the bottom
• Fraction

  A mixture of compounds with similar boiling points and similar sized molecules
• Cracking

  1. Breaks the larger fractions (for which supply exceeds demand) into smaller fractions (for which demand exceeds supply)

  2. Can also be used to produce large quantities of alkenes
• Thermal cracking

  • Uses high temperature (700-1200 K) and high pressure (7000 kPa)
  • Always produces one alkane, with all other molecules being alkenes
• Thermal cracking

  • C16H34 → C7H16 + C6H12 + C3H6
  • C16H34 → C8H18 + C2H4 + 2C3H6
• Catalytic cracking

  • Produces a high percentage of branched alkanes and cycloalkanes
  • Conditions: High temperature (720 K), slight pressure (around 100 kPa), zeolite catalyst
• Complete combustion of alkanes

  Alkanes react with excess oxygen to form carbon dioxide and water, releasing energy
• Complete combustion

  • C9H20 + 14O2 → 9CO2 + 10H2O
  • C7H16 + 11O2 → 7CO2 + 8H2O
• Incomplete combustion of alkanes

  In limited oxygen, produces carbon monoxide and solid carbon (soot) instead of carbon dioxide
• Incomplete combustion


  • C12H26 + 12.5O2 → 12CO + 13H2O
  • C4H8 + 2O2 → 4C + 4H2O
• Pollutants from alkane combustion

  • CO2 (greenhouse gas)
  • H2O (greenhouse gas)
  • CO (poisonous)
  • Solid C (damages lungs)
  • SO2 (acid rain)
  • NOx (acid rain)
  • Unburnt hydrocarbons (toxic, carcinogenic)
• Flue gas desulfurization


  1. Spraying a mixture of calcium oxide and water into the flue gas to react and make solid calcium sulfate

  2. Passing the flue gas through calcium carbonate to produce solid calcium sulfate
• Catalytic converters


  1. Honeycomb structure with platinum and rhodium catalysts

  2. Converts harmful CO and NO to less harmful N2 and CO2

  3. Converts unburned hydrocarbons and NO to less harmful CO2, H2O and N2