• Alkanes?are hydrocarbons that can be produced by the?addition?reaction?of hydrogen to an alkene or by?cracking?of longer alkane chains

Production of alkanes from addition reactions

• Alkenes are?unsaturated?organic molecules and contain C-C double bonds
• When?hydrogen?gas?and an?alkene?are?heated?and passed over a finely divided?Pt/Ni?catalyst, the addition reaction produces an alkane:
  • The Pt/Ni catalyst is finely divided to increase its surface area and therefore increase the rate of reaction
  • Eg.?butane?from?1-butene

• The addition reaction of alkenes with hydrogen is called?hydrogenation
• Hydrogenation is often used in the manufacture of?margarine?from?vegetable oil
  • Vegetable oil is an unsaturated organic molecule with many C-C double bonds
  • When these are partially hydrogenated, their hydrocarbon chains become straighter
  • This raises the melting point of the oils which is why margarine is a soft solid and vegetable oil a liquid at room temperature

Production of alkanes from cracking

• In?cracking?large, less useful hydrocarbon molecules found in crude oil are broken down into smaller, more useful molecules
• The large hydrocarbon molecules are fed into a?steel?chamber?and?heated?to a high temperature and then passed over an?aluminium?oxide?(Al2O3) catalyst
  • The chamber does not contain any?oxygen?to prevent?combustion?of the hydrocarbon to water and carbon dioxide
• When a large hydrocarbon is cracked, a?smaller?alkane?and?alkene?molecules are formed
  • Eg. octane and ethene from decane

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