Chemistry of the Air

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  • Chemistry of the Air
    • Global Warming
      • Greenhouse Gases include; CO2, CH4 and H2O
      • Greenhouse effect depends on 1) Atmospheric Concentration 2) Ability to absorb Infrared Radiation
      • Covalent bonds have various strengths due to different masses of the atoms and either end of the bond. Therefore, they vibrate at different frequencies
        • Frequency of Vibration can be found by detecting when the molecules absorb electro-magneitc radiation
        • Various types of vibrations are possible; Symmetric Stretching, Bending and Asymmetric Stretching
        • The frequencies and found in the infrared part of electro-magnetic spectrum and can be found using infrared spectroscopy
    • The Greenhouse Effect
      • Process; Radiation (Ultra Violet, Visible and Infra red) comes from the sun, 47% reaches the Earth's surface, Earth re-emits energy, 70% of re-emitted energy escapes
      • Increase conc. in greenhouse gases leads to GLOBAL WARMING
      • CCS (Carbon Capture and Storage) is when waste CO2 is...
        • 1) Injected as a liquid deep into oceans
        • 2) Stored in deep geographical formations
        • 3) Reacted with metal oxides to form carbonate minerals - e.g.  MgO + CO2  --> MgCO3
    • Depletion of the Ozone Layer
      • Ozone
        • Ozone is a reactive and poisonous gas but it protects us from harmful UV radiation which would affect life o Earth (e.g. Cancer)
        • Ozone in the stratosphere breaks down naturally -  2O3 --> 3O2
        • Ozone (trioxyen) can break up to give an ordinary oxygen and a radical - O3   --> O + O2
        • UV light supplies the energy for this process which is why the ozone layer is important
      • CFC's
        • CFC's break down in presense of UV light to form chlorine radicals - CCl2F2 --> Cl + CClF2
        • Chlorine radicals react with ozone - O3 + Cl --> ClO + O2
        • Chlroine radicals are regenerated - ClO + O --> O2 + Cl
      • NOx
        • Oxides of nitrogen (NOx) are formed during thunderstorms or by aircraft breakdown to give NO (nitrogen monoxide) which catalysis the break down of ozone
          • 1) O3 + NO   --> NO2 + O2
          • 2) NO2 + O   --> O2 + NO
    • Pollutant Gases from Internal Combustion Engines
      • CO, is formed by incomplete combustion of hydrocarbon. It is poisonous, combines with haemoglobin and prevents O2 being carried
      • NOx, formed by a combination of atmos nitrogen and oxygen under high temps. It aids photochemical smog (irritates eyes, nose and throat), aids formation of low level ozone which affects plant growth
      • CxHy, hydrocarbonsthat have not been combusted. They are toxic
    • Catalytic Converters
      • Operation
        • 2NO(g) + 2CO(g) --> N2(g) + 2CO2(g)
        • Unburnt hydrocarbons are converted into CO2 and H2O
        • Catalysts are rare metals -RHODIUM, PALLADIUM - which are finallly divided for greater surface area (more active sites)
      • Stages
        • 1) Adsorption; NO and CO seet out active sites on catalyst surface, they're bonds with surface weakens bonds in molecule, this makes reactions easier
        • 2) Reaction; Being held on surface increases chance of favourable collisions, bonds break and re-arrange
        • 3) Desorption; Products of N2 and CO2 are then released from the active sites

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