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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- 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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- 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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- 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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