C7 - organic chemistry

• hydrocarbons only contain hydrogen and carbon atoms
• alkanes have all C-C bonds
• alkanes are the simplest type of hydrocarbon you can get. they have a general formula CnH2+2. the alkanes are a homologous series a group of organic compounds that react in a similar way. alkanes are saturated compounds each carbon atoms form four single covalent bonds
• the first four alkanes are methane, ethane, propane and butane
• hydrocarbon properties change as the chain gets longer
• the shorter the carbon chain the more runny a hydrocarbon is that is the less viscous it is
• hydrocarbons with shorter carbon chains are also more volatile e.eg have low boiling points
• the shorter the hydrocarbon chain the more flammable it is
• the properties o hydrocarbons affect how they are used for fuels e.g short chained hydrocarbons with lower boiling points are used as bottled gases stored under pressure as liquids in bottles
• complete combustion : hydrocarbon + oxygen -- carbon dioxide + water
• duing combsution both carbon and hydrocarbon are oxidised
• hydrocarbons are used as fuels due to the amount of energy released when they combust completely
• crude oil is made over a long period of time
• crude oil is a fossil fuel it is formed from the remain of plants and animals mainly plankton, that died millions of years ago and were buried in mud. over millions of years with high temperatures and pressure the remains turn to crude oil which can be drilled up from rocks where it is found
• fossil fuels like coal, oil and gas are called non renewable fuels as they take so long to make that they are being used up much faster than they are being formed. they finite resources meaning they will run out one day
• fractional distillation can be used to separate hydrocarbon fractions
• crude oil is a mixture of lots of different hydrocarbons most of which are alkanes. the different compound in crude oil are separated by fractional distillation
• Fractional distillation of oil

  1. Oil is heated until most of it has turned to gas

  2. Gases enter a fractionating column

  3. Temperature gradient in the column - hot at the bottom, cooler at the top

  4. Longer hydrocarbons with high boiling points condense and drain out early near the bottom

  5. Shorter hydrocarbons with low boiling points condense and drain out later near the top
• Fractions


  Mixtures of hydrocarbons with similar numbers of carbon atoms and similar boiling points
• The crude oil mixture is separated into different fractions through fractional distillation
• oil provides fuel for transport
• the petrochemical industry uses hydrocarbon as a feedstock to make new compounds like polymers, solvents and lubricants
• cracking means spitting up long chain hydrocarbons
• longer alkanes molecules produced from fractional distillation are turned into smaller more useful ones this process is called cracking
• cracking is a thermal decomposition reaction - breaking down molecules down by heating them
• the first step is to heat a long chain of hydrocarbon to vaporise them turn them into gas. then the vapour is passed over a hot powdered aluminium oxide catalyst. the long chain molecules split apart on the surface of the specks of catalyst this is catalytic cracking. you can also crack hydrocarbons if you vaporise them mix them with steam and then heat them to a very high temperature this is known as steam cracking