Topic 7

• Hydrocarbons contain


  Only hydrogen and carbon atoms
• The alkanes are a homologous series
• Alkanes are saturated compounds
• The first four alkanes are 


  Methane

  ethane

  propane

  butane
• What's the general formula for alkanes


  CnH2n+2
• The shorter the hydrocarbon chain the more runny it is
• The shorter the carbon chain the more volatile it is (turns into a gas at a lower temperature)
• The longer the carbon chain, the harder to break down
• The longer the carbon chain, the less soluble it is in water
• The longer the carbon chain, the higher its boiling point
• Hydrocarbon + oxygen -> Co2 + H2O
• Complete combustion of any hydrocarbon in oxygen releases lots of energy
• The waste products for complete combustion, our carbon dioxide and water vapour
• During combustion, both carbon and hydrogen from the hydrocarbon are oxidised (oxidation can be defined as the gain of oxygen)
• Hydrocarbons are used as fuel due to the amount of energy released when they combust completely
• Crude oil is a fossil fuel formed from the remains of plants and animals that died millions of years ago and were buried in mud. It can be drilled up from the rocks where it is found
• Crude oil and other fossil fuels like coal oil and gas accord non-renewable food fuse as they take so long to make that they are being used up much faster than they are being formed they are finite
• Fractional distillation is used to separate hydrocarbon fractions
• Crude oil is a mixture of lots of different hydrocarbons most of which alkanes
• The different compounds include oil are separated by fractional distillation
• Fractional distillation


  1. Oil is heated until most has turned into gas

  2. Gases enter a fractionating column

  3. Temperature gradient in column (hot at bottom, cold at top)

  4. Longer hydrocarbons condense and drain out early near bottom

  5. Shorter hydrocarbons condense and drain out near top where it's cooler

  6. Crude oil mixture separated into different fractions
• Fractions


  Contain a mixture of hydrocarbons with similar number of carbon atoms and similar boiling points