Fuels

• What are hydrocarbons?

  • compounds that contain carbon and hydrogen only
• Describe crude oil

  • a complex mixture of hydrocarbons
  • containing molecules in which carbon atoms are in chains or rings
  • an important source of useful substances (fuels and feedstock for the petrochemical industry)
  • a finite resource
• What are the fractions from top to bottom?

  • gases
  • petrol
  • kerosene
  • diesel oil
  • fuel oil
  • bitumen
• What are the uses of gases?

  • domestic heating & cooking
• What are the uses of petrol?

  • fuel for cars
• What are the uses of kerosene?

  • fuel for aircraft
• What are the uses of diesel oil?

  • fuel for some cars and trains
• What are the uses of fuel oil?

  • fuel for large ships and in some power stations
• What are the uses of bitumen?

  • to surface roads and roofs
• What happens in the complete combustion of hydrocarbon fuels?

  • carbon dioxide and water are produced
  • energy is given out
• Homologous series

  • have the same general formula
  • differ by CH2 in molecular formula from neighbouring compounds
  • have similar chemical properties
  • show a gradual variation in physical properties, as exemplified by their boiling points
• Incomplete combustion of hydrocarbons

  • can produce carbon (in the form of soot) and carbon monoxide
  • as there's insufficient oxygen (limited supply) to oxidise all carbon to carbon dioxide
• How does carbon monoxide behave as a toxic gas?

  • reacts with haemoglobin in blood so stops oxygen being carried by red blood cells, less reaches the brain
• How is acid rain formed?

  • hydrocarbon contains sulfur impurities
  • sulfur burns at the same time as the hydrocarbon
  • sulfur reacts with oxygen
  • sulfur dioxide (acidic) gas is formed
  • sulfur dioxide dissolves in clouds to form sulfurous acid which is then oxidised to form sulfuric acid
  • rain water becomes acidic
• What are the problems with acid rain?

  • damages buildings and plants
  • runs into rivers
  • makes rivers acidic
  • kills fish
  • increases corrosion of metals
• What is methane?

  • a non-renewable fossil fuel found in natural gas
• What are the non-renewable fossil fuels obtained from crude oil?

  • petrol
  • kerosene
  • diesel oil
• What does cracking involve?

  • the breaking down of larger, saturated hydrocarbon molecules (alkanes) into smaller, more useful ones, some of which are unsaturated (alkenes)
  • requires a lot of energy as strong covalent bonds are broken
• why is cracking necessary?

  • there's more demand for products like petrol and diesel than for bitumen and fuel oil
  • also produces alkene molecules, which can be used to make polymers (mostly plastics)
• What are the problems with soot?

  • causes global warming - sea levels rising
  • reduces air quality so this particulate can cause breathing problems
  • makes buildings dirty
• What happens when fuels are burned in engines?

  • oxygen and nitrogen react together at high temperatures (provides energy) to produce nitrogen monoxide which is then released from vehicle exhaust systems and combines with oxygen in the air to form nitrogen dioxide
  • these oxides of nitrogen are pollutants
• What are the advantages of using hydrogen, rather than petrol, as a fuel in cars?

  • clean as only waste product is water
  • petrol is from crude oil, a finite resource
• What are the disadvantages of using hydrogen, rather than petrol, as a fuel in cars?

  • expensive
  • difficult to transport and store
  • dangerous because it can be explosive
• How is crude oil separated into simpler, more useful mixtures?

  • crude oil is heated before being passed into the fractional distillation column
  • during the distillation, vapour rises up the column until it is cold enough for the vapour to condense and form a liquid
• How do hydrocarbons in the bottom fractions differ from top?

  • more carbon atoms per molecule
  • so boiling point is higher because of the stronger intermolecular forces
  • harder to ignite so less flammable
  • high viscosity, not runny
• Why are fuels burnt?

  • to release energy