Alkanes

• What's the relationship between chain length, branching and the melting and boiling points?

  • As chain length increases so does mp/bp due to more intermolecular forces (van der waals)
  • More branches the less/weaker intermolecular forces so decreases mp/bp
• What is the purpose of cracking?

  • Makes use of the excess of long chain hydrocarbons to meet the demand for shorter hydrocarbons
• Conditions for thermal cracking

  • High temperature - up to 1000
  • High pressure - 70atm
  • Produces alkenes
• Conditions for catalytic cracking

  • High temperature - around 500
  • Low pressure
  • Zeolite catalyst
  • Aromatics, alkanes and fuels
• Equation for complete combustion of ethane

  C2H6 + 7/2O2 -> 2CO2 + 3H2O
• Incomplete combustion of propane to for carbon monoxide

  C3H8 + 7/2O2 -> 3CO + 4H2O
• Incomplete combustion of butane to produce carbon

  C4H10 + 5/2O2 -> 4C + 5H2O
• Why is flue gas necessary?

  • Sulfur impurities are burnt produce SO2 which cause acid rain
  • Removing the by flue gas desulfurisation prevents this (reacts it with CaO - neutralisation reaction)
• Why is Nitrogen reactive in a car engine but not in nature?

  • Usually unreactive but due to higher temperature and pressure it becomes reactive
• Equation for reaction of Nitrogen and oxygen

  N2 (g) + O2 (g) -> 2NO (g)
• Equation for the reaction in a catalytic converter

  2CO + 2NO -> 2CO2 + N2
• Why is the catalytic metal place on a honeycomb shape?

  Provides a large surface area for it to react on
• Equation for octane and Nitrogen monoxide

  C8H18 + 2NO -> 8CO2 + 25/2N2 + 9H2O
• Outline process of fraction distillation

  1. Crude oil is vaporised and feed into the fractional column which has a -ive temperature gradient
  2. The crude oil rises up the column the different fractions Condense at the boiling points and are then collected
  3. Short chains at the top, longer at the bottom