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The Greenhouse Effect

  • "The process in which the absorbtion and subsequent emission of infrared radiation by atmospheric gases warms the lower atomosphere and the planets surface".
  • The Earth's atomosphere contains traces on CH4, CO2, and H2O; these gases cause the Earth's temperature to be higher than it would usually be; they are known as Greenhouse Gases and absorb infrared energy in their bonds; causing them to vibrate. 
  • The C=O in carbon dioxide, the O-H in water and, C-H in methane.
  • The amount of energy which the substances absorb depends on two factors:
    -The concentration of the gases.
    -The gases' ability to absorb IR energy.
  • As the concentration of these Greenhouse Gases increases; more IR energy is absorbed so the Earth's atmosphere gets hotter.
  • Relative absorbance of IR is compared to CO2:
    -Methane is 30 times more absorbing.
    -CFC's absorb 10000-25000 times more.
  • These gases are increasing in concentration due to the burning of fossil fuels.
  • Chemists attempt to protect the environment by:
    -Cutting down CFC's.
    -Monitoring the effect of CO2 emissions by cars.
    -Investigating solutions to climate change. 
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  • Reduced reliance on fossil fuels:
    -Reduce the burning of fossil fuels.
    -Investigate alternative fuels.
    -Discontinue the destruction of rainforests (trees absorb CO2)
  • Carbon-Capture and Storage (CCS):
    -Collecting CO2 produced from power stations and storing it in underground systems.
  • Deep-Water Injection:
    -The CO2 can be liquified under high pressure and injected deep into the oceans.
    -HOWEVER this could acidify the oceans, disturbing the natural ecosystem.
    E.g. CO2 + H2O -> H2CO3 (weak acid).
  • Reaction with Metal Oxides:
    -Can be reacted with metal oxides to form stable carbonates:
    E.g. CaO + CO2 -> CaCO3.
  • Chemists are also working to:
    -Develop more efficient engines for transport.
    -Find uses for CO2. 
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Ozone Layer

  • The ozone layer is a layer of toxic gas (O3) in the stratasphere that absorbs UV radiation.
  • Mainained as such: O2 + O <-> O3
  • Radicals (formed by CFC's or NO from exhausts) disrupt this balance.
    E.g. CF3Cl -> CF3' + Cl'                1/2N2 + 1/2O2 -> NO'
  • These act as homogenous catalysts in the breakdown of the ozone (R = radical):
    R + O3 -> RO + O2
    RO + O -> R + O2
    OVERALL = O3 + O -> 2O2
  • CFC's are now widely used, but:
    -Still get used.
    -Take many years to reach ozone.
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Problem's With Internal Combustion Engines

  • Car engines are powered by burning fuels:
    E.g. C8H18 + 12.5O2 -> 8CO2 + 9H2O
  • However complete incomplete combustion occurs:
    E.g. C8H18 + 8.5O2 -> 8CO + 9H2O
  • Burning of hydrocarbons in car engines produces pollutants:
    -CO = Toxic gas
    -Unburnt hydrocarbons (benzene) = toxic and carcinogenic
    -NO's = forms acid rain and smog
  • Nitrous Oxides
    1/2N2 + 1/2O2 -> NO
    NO + 1/2O2 -> NO2 (This can then form nitric acid, for acid rain).
  • These also produce low-level ozone (toxic) and smog. 
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Catalytic Converters

  • Made up of three precious metals: platinum, palladium, and rhodium. 
  • These act as catalysts for:
    -Oxidation of unburnt hydrocarbons.
    -Reaction between nitrous oxides and carbon monoxide.
  • An example of a heterogenous catalyst as the catalyst is solid and the reactants are gases.
  • There are three steps:
    -Adsorption: Gas molecules adsorb onto (form a weak bond with) the surface of the catalyst.
    -Weakening of bonds: Within NO and CO the bonds are weakened so reactions are faster.
    -Desorption: The products N2 and CO2 are desorbedd from the surface to the atmosphere. 
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Other Information

  • Monitoring Air Pollution
    -IR spectroscopy can be used to detect CO, NO's and unburnt hydrocarbons.
    -An automated system that monitors the presence and detection of pollutants.
  • Green Chemistry (Five Principles)
    -Uses of processes that avoid using hazardous chemicals.
    -Designed for high atom economy.
    -Use of renewable (i.e. plant-based) resources.
    -Alternative energy sources (i.e. solar, tidal, wind, and geothermal).
    -Ensuring waste is non-toxic and can be recycled.
  • Role Of International Agreements
    -Montreal = Ban use of CFC's.
    -Rio = Emphasis on sustainable development.
    -Kyoto = Set limits of greenhouse gases production.
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