organic chemistry

• a hydrocarbon is any compound that is formed from carbon and hydrogen atoms only
• alkanes have all C-C single bonds
• alkanes are the simplest type of hydrocarbon you can get.
• alkanes have the general formula CnH2n+2
• what is the homologous series?

  a group of organic compounds that react in a similar way
• alkanes are saturated compounds - each carbon atom forms four single covalent bonds
• what are the four alkanes I need to know?

  methane, ethane, propane, butane
• As the length of the carbon chain changes, the properties of the hydrocarbon change
• the shorter the carbon chain, the more runny a hydrocarbon is (less viscous)
• hydrocarbons with shorter chains are more volatile
• the shorter the carbon chain, the more flammable the hydrocarbon is
• complete combustion happens when there is plenty of oxygen
• complete combustion of any hydrocarbon in oxygen releases lots of energy. The only waste products are carbon dioxide and water vapour
• crude oil is formed from the remains of plants and animals, mainly plankton
• crude oil forms over millions of years with high temperature and high pressure
• fractional distillation is used to separate hydrocarbon fractions
• what is the first step of fractional distillation?

  the oil is heated until most of it is gas, the gases enter a fractionating column
• in a fractionating column the longer carbons have higher boiling points so they condense back into liquids and drain out of the column early on, when they're near the bottom
• in a fractionating column the shorter hydrocarbons have a lower boiling point so condense and drain out much later on, near to the top of the column
• fractional distillation of crude oil gives you the crude oil mixture separated out into different fractions, each fraction contains a mixture of hydrocarbons that all contain a similar amount of carbon atoms so have similar boiling points
• short chain hydrocarbons are more flammable so make good fuels and are higher in demand
• long chain hydrocarbons form thick gloopy liquids like tar which aren't useful so a lot of the longer alkane molecules are turned into smaller more useful ones through cracking
• cracking is a thermal decomposition reaction - breaking molecules down by heating them
• catalytic cracking:

  1. heat long chain hydrocarbons to vaporise them
  2. the vapour is passed over a hot powdered aluminium oxide catalyst
  3. the long chain molecules split apart on the surface of the specks of catalyst - this is called catalytic cracking
• steam cracking:

  1. vaporise the long chain hydrocarbons
  2. mix them with steam
  3. heat them to a very high temperature
• alkenes have a C=C double bond
• alkenes are hydrocarbons which have a double bond between two of the carbon atoms in their chain
• The double C=C bond means that alkenes have two fewer hydrogens compared with alkanes containing the same number oof carbon atoms, this makes them unsaturated
• what are the alkenes I need to know?

  ethene, propene, butene, pentene
• ethene has two carbon atoms
• propene has three carbon atoms
• butene has four carbon atoms
• pentene has five carbon atoms
• alkenes burn with a smoky flame
• in a large amount of oxygen, alkenes combust completely to produce only water and carbon dioxide
• if there isn't enough oxygen for complete combustion to take place, alkenes undergo incomplete combustion. Carbon dioxide and water are still produced, but you can also get carbon and carbon monoxide
• incomplete combustion results in a smoky yellow flame and less energy being released compared to complete combustion of the same compound
• alkenes react via addition reactions
• a functional group is a group of atoms in a molecule that determine how that molecule typically reacts.
• all alkenes have the functional group 'C=C' so they all react in similar ways