3.2 Alkanes

Alkanes are the main constituent of crude oil, which is an important raw material for the chemical industry.
Alkanes are also used as fuels and the environmental consequences of this use are considered in this section.

  • Bunsen flames Hydrocarbon fuels - Before embarking on this topic, there is a great award winning video to mention, that is definitely worth watching: 300 years of fossil fuels in 300 seconds. [click here] What is a hydrocarbon fuel?  This is a fuel containing molecules of hydrocarbons. A hydrocarbon is a compound containing carbon and hydrogen atoms only.  In most cases, a hydrocarbon fuel refers to fossil
  • Fractional distillation of crude oil (GCSE) - Crude oil contains a mixture of different hydrocarbon compounds that boil at different temperatures. The larger the hydrocarbon molecule (the longer its carbon-chain length), the higher its boiling point. Liquids boil (liquid→gas) at their boiling point and start to condense (gas→liquid) back to liquid just below this temperature. Cooling encourages condensation. What is the difference between distillation and fractional distillation? For
  • Fractional distillation of crude oil (AS) - Alkanes are saturated hydrocarbons. Petroleum is a mixture consisting mainly of alkane hydrocarbons that can be separated by fractional distillation. Different components (fractions) of this mixture can be drawn off at different levels in a fractionating column because of the temperature gradient Assessment and practical opportunities Fractional distillation of a crude oil substitute.
  • Modification of alkanes by cracking - Cracking involves breaking C–C bonds in alkanes. Catalytic cracking takes place at a slight pressure, high temperature and in the presence of a zeolite catalyst and is used mainly to produce motor fuels and aromatic hydrocarbons (mechanism not required). Thermal cracking takes place at high pressure and high temperature and produces a high percentage of alkenes (mechanism not required). Students should be able to explain the
  • Combustion of alkanes - Alkanes are used as fuels. Combustion of fossil fuels (including alkanes) results in the release of carbon dioxide into the atmosphere Carbon dioxide, methane and water vapour are referred to as greenhouse gases and that these gases may contribute to global warming Combustion of alkanes and other organic compounds can be complete or incomplete. The internal combustion engine produces a number
  • Chlorination of alkanes - Synthesis of chloroalkanes The reaction of methane with chlorine. Students should be able to: explain this reaction as a free-radical substitution mechanism involving initiation, propagation and termination steps. Chloroalkanes and chlorofluoroalkanes can be used as solvents
  • Obtaining useful substances from crude oil (cracking) - Cracking (type of thermal decomposition) Hydrocarbons can be cracked (decomposed) to produce smaller, more useful molecules. There are two types of cracking process that achieve thermal decomposition: catalytic cracking and thermal cracking. Catalytic cracking: the alkane is heated and the vapour is passed over a hot zeolite (aluminosilicate) catalyst. The reaction occurs at around 500ºC. Thermal (steam) cracking: the alkane vapour