7-Organic chemistry

• organic chemistry is about molecules that contain carbon
• hydrocarbons are any compound that is formed from only hydrogen and carbon
• alkanes

  • alkanes are a group of the most simple types of hydrocarbons
  • the general formula for alkanes - Cn H2n+2
  • the first four hydrocarbons are: methane, ethane, propane, butane
  • they are saturated compounds - every carbon atom has four single covalent bonds - NO double bonds
  • example of a homologous series - a group of organic compounds that have similar chemical properties so can have a formula
• isomers are molecules that have the same molecular formula but different structural formulas - they are made of the same atoms but are arranged differently
• properties of alkanes

  • melting and boiling point increase as they get longer
  • viscosity increases as they get longer (thickness)
  • volatility decreases as they get longer (how easily it vaporizes)
  • flammability decreases as they get longer
  • they have weaker intermolecular forces when they are shorter, there is more when they are longer
• combustion reactions

  • fuel - main use of alkanes as they release lots of energy when burned with oxygen
  • this results in complete combustion - hydrocarbon + oxygen = carbon dioxide + water
  • it is an exothermic reaction
  • the hydrogen and carbon are oxidised as they combine with oxygen
• crude oil

  • crude oil is a fossil fuel and is a mixture of different compounds, mainly made up of hydrocarbons
  • crude oil is naturally formed - from the remains of dead plants and animals, particularly plankton, that died millions of years ago - they were buried in the earth - compressed under heat and pressure - developed into crude oil
  • it is a finite resource as it takes so long to form
  • fractional distillation - separate it's hydrocarbons
• fractional distillation

  • shorter chain hydrocarbons condense at the top as they have lower boiling points
  • longer chain hydrocarbons condense at the bottom as they have higher boiling points
  • they range in how many bonds have to break
• fractional distillation

  • hydrocarbons are separated from crude oil in fractionating column as they have different properties

  1. heat crude oil - compounds are gaseous
  2. hydrocarbons rise - hot gas rises
  3. they cool as they rise - column is cooler at top
  4. hydrocarbons condense - they pass their boiling point
  5. the liquid is collected
• fractionating column

  • used to separate crude oil so that hydrocarbons can be made useful

  A) gas

  B) petrol

  C) kerosine

  D) diesel

  E) fuel oil

  F) bitumen

  G) cooler

  H) hot

  
• fractional distillation - hydrocarbon uses

  • gas - liquified petroleum gases contains propane and butane, fuel for domestic heating and cooking
  • petrol - fuel for cars and other vehicles
  • kerosine - fuel for aircrafts
  • diesel - fuel for cars and other vehicles
  • fuel oil - fuel for ships and power stations, can be separated further and then used heating, fuel or lubricating oil
  • bitumen - used for roads and roofs
• • feedstock is raw material used to provide reactants for an industrial reaction (the different hydrocarbons)
  • petrochemical is a substance made from crude oil by a chemical reaction (useful things made from hydrocarbons) - polymers, solvents, lubricants, detergents
• cracking

  • cracking is a process that longer chained, less useful hydrocarbons go through to break them into shorter, more useful hydrocarbons
  • cracking is a thermal decomposition reaction - breaking down molecules by heating them
  • ways to crack hydrocarbons - catalytic, steam
  • When a long chain alkane cracked, there aren't enough hydrogen atoms to make two alkanes so cracking will always produce one alkane and one alkene
• • catalytic cracking - pass hydrocarbon vapour over hot powdered aluminium oxide, catalysts causes hydrocarbon to split apart into 2 hydrocarbons
  • steam cracking - mix hydrocarbon vapour with steam and heat them to a very high temperature, this causes the hydrocarbon chain to split into 2 shorter ones
• cracking - balanced chemical equations

  • long chain alkane = shorter alkane + alkene

  A) C8H18

  
• alkenes

  • an example of a homologous series like alkanes
  • alkenes have a double bond between two carbon atoms - they are unsaturated
  • alkenes are more reactive than alkanes and can react with bromine - alkene solution turns bromine water from orange to colourless
  • alkenes can be added together to make polymers because their double bonds can break to form two or more bonds