Alkanes

• Homologus Series

  Compounds which have the same general formula, similar chemical properties, show gradation in their physical properties and successive members differ by a CH2 unit.
• What is the gneral formula for alkanes?

  CnH2n+2
• What are the different types of formula?

  Molecular, structural, condensed structural, emperical and skeletal.
• Structural Isomers

  Molecules with the same molecular formula but a different structural formula.
• What are the physical properties of alkanes?

  . Melting / boiling point increases as the number of carbon atoms increases.

  . Non polae molecules and experience only van der Waal's forces between neighbouring molecules. (gets stronger as the number of electrons in the molecule increases).
• Why do branches isomers have a lower boiling point than straight chained isomers?

  Branched isomers can't pack as close together resulting in fewer points of contacts between the molecules. This means there are weaker van der Waal's forces between the molecules.
• Combustion

  The chemical reaction of fuels with oxygen, releasing heat and forming oxides.
• What does complete combustion produce?

  Water and carbon dioxide
• What is the general equation for finding the formula of a hydrocarbon?

  CxHy + [x + y ] O2 -----> xCO2 + y H2O

  [ --] --

  [ 4 ] 2
• What does incomplete combustion produce?

  Water and carbon monoxide (soot is not included in the equation)
• How do the colours of combustion flames relate to carbon content?

  Smoky orange = high carbon content

  Clean blue = low carbon content
• How much carbon dioxide is there in the atmosphere?

  Between 0.03 and 0.04%
• How can you limit the production of greenhouse gases?

  . Remove sulfur from fuels before burning

  . Use a catalytic converter in you car

  . Scrub emissions with alkali from power stations / factories

  . Use renewable energy (solar, wind, wave)
• What are the equations for catalytic converters using reduction?

  2NO -> N2 + O2

  2NO2 -> N2 + 2O2
• What are the equations for catalytic converters using oxidation?

  2CO + O2 -> 2CO2
• What are the effects of carbon monoxide?

  Accute breathing difficulties
• Describe the structure of catalytic converters.

  A honeycomb structure coated in metal catalysts such as platinum(Pt).

  The metal coating keeps costs down as lees is used and the honeycomb structure gives it a larger surface area.
• Heterogeneous Catalysis

  A reaction in which the catalyst is in a different physical state than the reactants.
• Free Radical

  An atom, molecule or ion with an unpaired electron
• What is the first stage mechanism for the halogenation of alkanes?

  Initiation. (molecule -> radical)

  UV Light .

  Cl2 -------> 2Cl = Cl2 undergoes homolytic fission
• Homolytic Fission

  Bond breaking in which one of the shared electrons goes to each atom.
• What is the second mechanism stage for the halogenation of alkanes?

  Propogation (molecule + radical -> radical + molecule)

  . .

  Cl + CH4 -> HCl + CH3

  . .

  CH3 + Cl2 -> CH3Cl + Cl
• What is the third mechanism stage for the halogenation of alkanes?

  Termination (radicals -> molecules)

  . .

  Cl + Cl -> Cl2

  . .

  CH3 + CH3 -> C2H6

  . .

  Cl + CH3 -> CH3Cl