ALKENES

• Crude oil is a mixture of different hydrocarbons that can be separated by fractional distillation due to the different boiling points of molecules with varying chain lengths
• In fractional distillation:

  • The mixture is vapourised and fed into the fractionating column
  • Vapours rise, cool, and condense
  • Products with short carbon chains have lower boiling points and are collected at the top, while those with long carbon chains have higher boiling points and are collected at the bottom
  • Compounds collected are further broken down via cracking
• Cracking breaks down longer carbon chains into smaller, more useful molecules by breaking carbon-carbon bonds under harsh conditions
• Thermal cracking produces a high proportion of alkanes and alkenes at high temperatures and pressures, while catalytic cracking produces aromatic compounds with carbon rings at lower temperatures with a zeolite catalyst
• Alkanes are good fuels as they release a lot of energy when burned, undergoing complete combustion with sufficient oxygen to produce carbon dioxide and water
• Incomplete combustion of alkanes due to insufficient oxygen produces carbon monoxide alongside water, which can be harmful to humans
• Carbon monoxide and oxides of nitrogen produced from alkane combustion can be removed using a catalytic converter with a rhodium catalyst to convert them into more stable products like CO2 or H2O
• Incomplete combustion can also produce carbon particulates, small fragments of unburned hydrocarbon, which can cause serious respiratory problems if not removed from waste products
• Sulfur impurities in alkanes can lead to acidification of water in the Earth's atmosphere, which can be removed via flue gas desulfurisation using calcium oxide and gypsum
• Alkanes react with halogens in the presence of UV light to produce halogenoalkanes through a series of reactions involving free radicals called chlorination of alkanes
• Chlorination of alkanes involves initiation (halogen breakdown), propagation (hydrogen replacement), and termination (radicals join) steps, favoring termination to limit the number of substitutions in the chain reaction