3.3.2.3 Combustion of alkanes

• What can alkanes be used as?

  Fuels
• What is complete combustion?

  Chemical reaction when a fuel reacts with oxygen to form CO2 and hydrogen, exothermic,
• What must happen to alkanes before they burn?

  Become vaporised
• What is incomplete combustion?


  Limited supply of oxygen, carbon monoxide, soot, hydrogen
• Cracking of C15H32 into propene, butene and an alkane?

  C15H32 = C3H6 + C4H8 + C8H18
• Reforming of octane to cyclooctane?

  C8H18 = C8H16 + H2
• Difference between complete and incomplete combustion?

  Complete releases CO2, but has oxygen, incomplete has a limited oxygen supply
• 3 pollutant formed in incomplete combustion?

  Carbon monoxide, soot, unburnt hydrocarbons
• What happens once CO2 is released into the atmosphere?

  Enhances the greenhouse effect, global warming, climate change
• Types of the chemicals released?

  Carbon monoxide, caron particulates, oxides of nitrogen, sulfur impurities
• Problems of carbon monoxide?

  Prevents red blood cells from carrying oxygen around the body, haemoglobin, poisonous gas
• Example of carbon particulates?

  Soot
• Problems of carbon particulates?

  Dirty buildings, breathing problems, respiratory problems, build up in engines reduce efficiency
• Problems of oxides in nitrogen?

  Acid rain by dissolving in moisture forming H2NO3, causes smog, irritates eyes, lung damage, reacts with unburnt hydrocarbons in UV form ground-level ozone CO3
• Conditions that enable nitrogen oxides to be formed?

  High temperatures and pressure, hot engine causes nitrogen and oxygen to be formed
• Problems of sulfur impurities?

  Present in fossil fuels and gets oxidised to form SO2 leading to acid rain, dissolves in air moisture, converts to H2SO4, destroys trees, vegetation, corrodes buildings, fishes in lakes
• How can sulfur impurities be removed from power stations?

  By using calcium oxide to form CaSO3
• What's the use of catalytic converters in cars with petrol engines?

  Reduce the output of CO, NO, and unburnt hydrocarbons in the exhaust gas mixture
• Gases from the engine?

  CO, NO3
• Catalysts used?

  Platinum, which is expensive due to a shortage
• Gases to tailpipe?

  N2 + CO2
• What type of structure is used in a catalytic converter?

  Honeycomb
• Why is a honeycomb structure used?

  Permeable, gases can easily travel through and escape easily
• Why are the catalysts spread in a thin layer on a ceramic honeycomb?

  Increases the surface area to capture as much gas for catalytic removal
• How can oxides of nitrogen form in a car engine?

  High temperatures and pressure in a hot engine makes nitrogen oxide
• Why does nitrogen undergo these reactions at room temperature?

  Activation energy and triple bonds
• Effect of catalyst on rate of a chemical reaction?

  Lowers activation energy, more successful collisions
• Conversion of NO and CO to N2 and CO2?

  2NO + 2CO = 2CO2 + N2
• Why water has a much higher boiling point than other group 6 hydrides?

  Hydrogen bonding, strong intermolecular forces, more energy needed to overcome
• Reaction of calcium oxide and sulphur dioxide?

  CaO + SO2 = CaSO3
• Define an isomer?

  2 or more compounds with the same molecular formula, but a different arrangement of atoms in the molecule
• Products in catalytic convertors?

  Carbon dioxide, nitrogen, water
• What do molecules that have polar bonds absorb?

  Infrared radiation to make bonds vibrate
• Why can't N2 and O2 absorb infrared radiation?

  They aren't greenhouse gases and have no polar bonds
• Examples of polar molecules?

  CO2, H2O
• How to increase methane levels?

  Agriculture, farming
• How can sulfur be removed?

  Desulfurisation
• Process of desulfurisation

  Passed through a wet semi-solid mixture containing calcium carbonate and calcium oxide
• Calcium carbonate and calcium oxide are?

  Bases
• What is formed once S is passed through CaCO3 and CaO

  Calcium sulphite is oxidised to form calcium sulphate