organic

• a functional group is an atom or a group of atoms that determine the chemical properties of a compound
• a homologous series is a group of substances with:

  • the same general formula
  • similar chemical properties
  • a trend in physical properties
• isomers are molecules with the same molecular formula but with a different structure
• number of carbon atoms:

  1. meth-
  2. eth-
  3. prop-
  4. but-
  5. pent-
  6. hex-
• alkanes have the general formula CnH2n+2
• saturated: a molecule containing only single bonds between carbon atoms (alkanes)
• alkanes react with halogens in the presence of UV light. this is a substitution reaction
• alkane + halogen -(UVlight)> halogenoalkane + hydrogen halide
• alkenes have the general formula CnH2n and contain the functional group >C=C<
• unsaturated: a molecule containing a carbon-carbon double or triple bond (alkenes)
• ethene + bromine -> 1,2-dibromoethane
• alkenes react with bromine water without the presence of UV light (orange -> colourless)
• crude oil is a mixture of hydrocarbons
• crude oil separated by fractional distillation:

  • heated, oil evaporates
  • gas goes into fractional distillation tower. as the gas rises the temperature falls
  • fractions with higher boiling points condense and are collected nearer the bottoms of the tower
• uses for fractions:

  • refinery gases = bottled gas
  • gasoline = car fuel
  • kerosene = plane fuel
  • diesel oil = lorry fuel
  • fuel oil = ship fuel
  • bitumen = road surfacing
• as the fractions increase in size, their boiling points & viscosity increase, as well as getting darker in colour (R,G,K,D,F,B)
• a fuel is a substance that releases heat energy when burned
• complete combustion produces CO2 + H2O whereas incomplete combustion produces CO + H2O
• when fuels are burned at high temperatures in engines, nitrogen and oxygen from the air react to produce nitrogen oxides
• cracking involves the thermal decomposition of long-chain alkanes into shorter-chain alkanes and alkenes
• conditions for cracking:

  • 600 - 700°C
  • aluminium oxide (catalyst)