3.2 Alkanes

• What are alkanes

  Saturated hydrocarbons with the general formula CnH2n+2
• What is the boiling point of an alkane dependent on?

  The length of the chain as the longer the chain the greater number of electrons therefore stronger Van der Waals so the higher boiling points
• What is crude oil?

  Fossil fuels formed from the breakdown of plant and animal remains that have been subjected to high pressure
• What is fractional distillation?

  Will separate crude oil into different fractions?
• What is a fraction?

  A group of hydrocarbons that have a similar boiling point
• Give an equation to show complete combustion of an alkane using propane?

  C3H8(g) + 5O2(g) -> 3CO2(g) + 4H2O(g)
• What does incomplete combustion of an alkane produce?

  Carbon, carbon monoxide and unburned hydrocarbons
• How do you remove sulfur dioxide from flue gases? Give equations.

  Using calcium oxide or calcium carbonate

  
  

  CaO(s) + 2H2O(l) + SO2(g) -> CaSO3(s) + 2H2O(l)

  CaCO3(s) + 2H2O(l) + SO2(g) -> CaSO3(s) + 2H2O(l) + CO2(g)
• What do catalytic converters do?

  Remove gaseous pollutants from internal combustion engines by using precious metals spread over a mesh to form less harmful products such as N2, CO2 and H2O
• What is cracking used for?

  Converting longer chain hydrocarbons to more economically valuable shorter chain hydrocarbons
• What is thermal cracking?

  Alkanes are heated to high temperatures under high pressures. C-C bonds break and free radicals are formed. These react to form short chain hydrocarbons including at least one alkene
• What are the conditions for thermal cracking?

  High temperature (750 degrees Celsius)

  High pressure of 70atm
• What is catalytic cracking?


  Alkanes are heated to lower temperatures under lower pressures and passed over a zeolite catalysts consisting of SiO2 and Al2O3. This method is used mainly to produce motor fuels and aromatic compounds
• What are the conditions for catalytic cracking?

  Slight pressure

  High temperature

  Zeolite catalyst