Organic Chemistry

• Hydrocarbons are compounds made up of carbon and hydrogen atoms only.
• The general formula for alkanes is CnH2n+2
• Alkanes have single carbon bonds
• The alkanes are a homologous series
• A homologous series is a group of compounds that have similar properties and so react in a similar way due to them having the same functional group
• Alkanes are saturated meaning each C atom forms 4 single covalent bonds
• The first 4 alkanes are methane, ethane, propane, butane
• As chain length increases, the boiling point increases
• Shorter alkanes are more volatile and longer alkanes are more viscous
• Shorter alkanes are more flammable
• Complete combustion only occurs when there is sufficient oxygen
• Hydrocarbon + oxygen > carbon dioxide + water (+energy)
• Hydrocarbons are used as fuels due to the amount of fuel released when they combust completely
• Crude oil is a fossil fuel that is formed from the remains of ancient organisms
• Crude oil is made up of a mixture of hydrocarbons, mostly alkanes, which can be separated out by fractional distillation
• Fractional distillation

  • Heat the oil till it turns into a gas
  • There is a temperature gradient in the fractionating column
  • As the gases rise they will condense into a liquid if it is not hot enough and pass out the column
  • Longer hydrocarbons have the highest bps so condense early on (heavy fuel oil: heating oil, fuel oil, lubricating oil)
  • Shorter hydrocarbons will rise up the column and condense later on (Diesel, petrol, kerosene)
  • The shortest hydrocarbons will stay as a gas (Liquified petroleum gas: mostly propane and butane)
• A feedstock is a raw material used to provide reactants for an industrial reaction.
• A petrochemical is a substance made from crude oil, via chemical reactions.
• Cracking is a thermal decomposition reaction when longer hydrocarbons are broken down into smaller molecules so they can be used
• Catalytic cracking is when the vaporised hydrocarbons are passed over a hot powdered aluminium oxide catalyst which causes them to split apart on the surface of the catalyst
• Steam cracking is when the vaporised hydrocarbons are mixed with steam and then heated again to a very high temperature cauing them to split apart
• Alkenes are also a homologous series but are unsaturated as they have a double carbon bond
• Alkenes are more reactive than alkanes
• Test for alkenes: they should turn bromine water (orange) to colourless
• Alkenes can turn into polymers as the double bonds can break to form 2 or more bonds
• Addition reactions occur between an alkene and another molecule, forming a new compound where both atoms join together
• Alkenes: ethene, propene, butene, pentene
• General formula for alkenes: CnH2n