Hydrocarbons

Hydrocarbons

1. Any molecule that is formed from carbon and hydrogen atoms only

2. Properties

   • Flammability
     • How easily it burns
       • As the size of the molecule increases the flammability decreases
   • Boiling point
     • How easily the gas condenses or liquid boiks
       • As the size of the molecule increases the boiling point increases
   • Viscosity
     • The lack of fluidity in a substance
       • As the size of the molecule increases the viscosity increases
   • Volatility
     • The tendency to turn into gas
       • As the sides of the molecule increases the volatility decreases

3. Alkanes

   • Alkanes are saturated hydrocarbons
   • General formula of alkanes
     • CnH2n+2
   • First four alkanes
     • Methane
       • CH4
     • Ethane
       • C2H6
     • Propane
       • C3H8
     • Butane
       • C4H10

4. Fossil fuels

   • Finite non renewable resources
     • Burned in power stations to generate electricity
   • Formation
     • The remains of microscopic animals and plants were buried in sediments
       • The sediments built up burying the remains deeper and deeper
         • Caused acts of heat and pressure to convert the material into coal and natural gas and oil
       • The sediments excluded the air
         • Kept oxygen away
   • Coal
     • Carboniferous rock that is mainly made up of carbon which often has sulphur dioxide impurities
       • Uses
         • Fuek
         • Generate elwrrifity
         • Formation
           • Formed by the act of heat and pressure on plants and trees
   • Oul
     • Uses
       • Cooking
       • Fuels
       • Generating electricity
       • Economy
       • Heating homes
       • Running cars
     • Formation
       • Formed by the act of heat and pressure on sea plants and animals
   • Natural gas
     • Mainly methane
     • Uses
       • Bunsen burners
       • Central heating
       • Burned in some power stations
     • Formatiob
       • Formed by the act of heat and pressure on sea animals and plants

5. Crude oil

   • Dark, thick, pungent liquid
     • Varies in colour from colourless to black
   • Mixture of many compounds which are mainly hydrocarbons, the majority of which are alkanes
     • They can be separated into the hydrocarbon compounds by fractional distillation
       • This works because there are a mixture of compounds which means a mixture of different sized hydrocarbon molecules with different boiling points and therefore they condense at different temperatures
   • Formation
     • The remains of microcosmic animals and plants fell to the bottom of the sea
       • They were then covered by layers of mud and as the layers of mud built up it pushed them deeper and deeper until the actions of heat and pressure changed them into rock
         • The decaying remains were then slowly converted into crude oil in the absence of oxygen causing the bacteria to respire anaerobically
           • As the oil is less dense than the water underneath it, it rose through the layers of porous rock
             • Earth movements cause the rock to be split and the crude oil to be trapped underneath layers of non porous rock
               • The oil became trapped underground with natural gas in pockets above or in it and when drilled it escapes to the surface

6. Fractional distillation of crude oil

   • Crude oil can be separated into the compounds it is made from by fractional distillation as it contains a mixture of compounds with different sized molecules and different boiling points
   • It can be done in a lab but the collection vessel must be changed to collect the fractions as the temperature rises
   • The hydrocarbons with the smallest molecules are collected nearer the top
     • Smaller molecules means smaller boiling point
       • Rise more before condensing
       • Condense at a lower temperature
   • The hydrocarbons with the largest molecules are collected nearer the bottom
     • Larger molecules means larger boiling point
       • Don’t have to ride as much before condensing
   • Process
     • Crude oil is heated until it boils in a furnace underneath the fractionating column
       • It is vaporised and enters the fractionating column as a gas
         • The fractionating column has trays in with holes in to allow the gases to rise to the section cooled to their boiling point
           • The fractionating column ha as temperature gradient meaning that the temperature decreases as the height increases
             • When the age reaches the level of their boiling point they are condensed into a liquid
               • The fractions can be collected and different fractions can be piped off at the levels at which they condense
                 • They can be piped away into different storage containers
   • Products
     • C1-c4 gases
       • LPG
         • Liquified petroleum gas
     • C5-c9
       • Naphtha
     • C5-c10
     • C10-c16
     • C14-c20
     • C20-c50
     • C20-c70