Alkanes

    Cards (20)

    • general formula of alkane - C n H 2n+2
    • Alkanes and cycloalkanes are saturated hydrocarbons because they contain no double bonds / maximum number of hydrogen atoms
    • Hydrocarbons are usually obtained from fractional distillation of crude oil
    • Fractions - molecules with similar number of carbon atoms in their chains
      They are separated due to the difference in their boiling temperature
    • Reforming - processing of straight chain hydrocarbon into branched-chain alkanes and cyclic hydrocarbons for efficient combustion
    • Pollutants
      • carbon monoxide (toxic - reduce capacity of oxygen in RBC)
      • oxides of nitrogen (acid rain)
      • oxides of sulfur (acid rain - H2SO4)
      • unburnt hydrocarbons
      • carbon particulates
      Are formed during combustion of alkane fuels
    • Catalytic converter uses a rhodium catalyst
      • absorbs, reacts, desorbs
      • turns 2NO -> N2 + O2
      • turns 2CO + O2 -> 2CO2
      • turns 2NO2 -> N2 + 2O2
    • Acid rain consequences
      • damage to aquatic life in lakes / rivers
      • damage to crops and forests
      • damage to buildings / structures made of marble or limestone
    • Fractions - molecules with similar number of carbon atoms in their chainsThey are separated due to the difference in their boiling temperature
    • Alternative fuels
      • biofuels release fewer and less harmful products (but release CO2 = greenhouse gas = contributes to climate change)
      • ethanol is an example of a biofuel - carbon neutral (crops need to be grown, fermented for ethanol) + low percentage yield
      • however sustainable - and renewable so wont run out
    • A radical
      • species with an unpaired electron and is represented in mechanisms by a single dot
      • formed by homolytic fission of a covalent bond
    • Free radical substitution with Halogens (UV LIGHT)
      CH4 + Cl2 -> CH3Cl + HCl
    • Free radical substitution (initiation propogation termination)
      • UV radiation causes homolytic fission
      • Cl2 -> 2Cl*
    • Free radical substitution PROPAGATION
      • Cl* + CH4 -> *CH3 + HCl
      • *CH3 + Cl2 -> CH3Cl + Cl*
    • Free radical substitution (termination)
      • *CH3 + *CH3 -> C2H6
      • Cl* + Cl* -> Cl2
      • *CH3 + Cl* -> CH3CL
    • Free Radical Substitution is not efficient
      • difficult to control
      • excess halogen present
      • mixture of products
      • needs to be fractionally distilled - costly
    • Boiling vs melting point of alkanes
      • (boiling)
      • as the number of carbon atoms increases, the number of electrons increases, the strength of London forces increases, and boiling temperature increases
      • (melting)
      • EVEN NUMBER CARBON vs ODD NUMBER CARBON
      • even-numbered chains pack together more efficiently - the melting point is higher
    • Alkanes are insoluble in water
      no hydrogen bonding possible
      Alkanes are soluble in non polar solvent
    • Octane rating or octane number is a standard measure of the performance of an engine or aviation fuel.
      HIgher the octane number, the more compressible the fuel can withstand before combustion
    • Why do branched chains have lower boiling points
      • branched chains have lower surface area
      • so the London forces are weaker