Module 4

• Alkane


  All bonds are full so it is saturated

  Covalently bonded
• Alkane formula


  CnH2n+2
• Alkene


  More reactive

  Double bonded carbons

  Unsaturated (mono)
• Alkene formula


  CnH2n
• Making fuel (complete combustion equation)

  fuel + O2 >>>>> CO2 + H2O
• Making fuel (incomplete combustion equation)

  fuel + O2 >>>>> CO + H2O
• Making fuel (really incomplete combustion equation)


  fuel + O2 >>>>> C + H2O
• Skeletal formula


  You just draw the basic backbone of the molecule

  Each bend is a main element
• Isomers


  Skeletal formulas with one less straight line but an extra branch
• Difference between straight chain and branched alkanes

  Straight chains are more likely to be incomplete combusted and they are harder to break due to London forces.

  Branched are easier to break
• Cracking


  Splits long chain alkanes into shorter chain alkanes: alkenes and hydrogen

  2 main types: thermal and catalytic

  Increases economically important fractions
• Thermal cracking


  High temperature (700 - 1200K)

  High pressure (7000KPa)

  A carbon-carbon bond breaks and one electron from the pair goes to each carbon atom
• Catalytic cracking


  Only needs a bit of pressure

  700K temperature

  More branched chains are made

  Used to make more expensive petrol

  e.g. of a catalyst: zeolite
• Dynamic equilibrium


  Both forward and reverse reactions are ongoing

  Rates of both are the same

  Concentrations of the components remain constant
• Le Chatelier's principle


  If a factor affecting the position of an equilibrium is altered, the position of the equilibrium shifts to oppose the effect of the change
• Equilibrium for concentration


  Increase - moves to the right

  Decrease - moves to the left
• Equilibrium for pressure


  Increase - moves to the side with the fewest mols

  Decrease - moves to the side with the most mols

  Same mols - no effect
• Equilibrium for temperature


  Increase - moves to the left

  Decrease - moves to the right
• Equilibrium for catalysts


  No change in equilibrium

  Faster reaction
• Forward reaction


  Exothermic
• Reverse reaction


  Endothermic
• How is ethanol made

  The hydration of ethene
• Haber process


  Producing ammonia
• Ammonia


  Used as a fertiliser
• Equilibrium constant equation


  Kc = [C]^c x [D]^d / [B]^b x [A]^a

  
  

  Kc > 1 means it lies to the right

  Kc < 1 means it lies to the left
• Positional isomers


  Alkenes with four or more carbon atoms
• Sigma bond


  Single bond

  End to end orbitals overlap

  Strongest type of covalent bond
• Pi bond


  Double bond

  Sideways overlap of orbitals

  Electron density is less

  Not as strong
• Electrophilic ions


  Positive or delta positive

  Attracted to pi bonds
• Electrophilic addition


  Electrophile must be either positive or delta positive

  Can also be an instantaneous dipole or an induced dipole
• Double headed arrow


  Show that two electrons are given
• Single headed arrow


  Show that one electron is given
• Fermentation


  Low atom economy

  Not good for the environment

  Produces CO2

  Lower yield
• Hydration


  100% atom economy

  Steam and acid as a catalyst

  Continuous process

  High yield
• Alcohols


  Homologous series

  General formula: CnH2n+1OH

  Ending in -ol

  Higher boiling point than alkanes
• Hydroxyl group


  Functional group of alcohols

  Electronegative oxygen making them polar

  Take place in hydrogen bonding
• R group


  Representation of a chain of carbon atoms
• Single headed arrow
• Secondary (2) alcohols


  Two R groups attached to the carbon
• Tertiary (3) alcohols


  Three R groups attached to the carbon