Reducing the Effects of Environmental Issues (Cambridge (CIE) O Level Chemistry) : Revision Note

Reducing the Effects of Environmental Issues

• The effects of climate change and acid rain are far reaching and strategies are needed to reduce their impact

Dealing with Climate Change

• The production of greenhouse gases needs to be reduced drastically to avoid or at least slow climate change

• CO₂ emissions can be reduced by using hydrogen and renewable energy supplies such as solar or wind energy instead of burning fossil fuels

• Reducing the amount of livestock farming would decrease the methane emissions produced from digestion in animals

• Planting more trees would remove more carbon dioxide from the atmosphere

Dealing with Acid Rain

• Acid rain is caused by oxides of nitrogen and sulfur dioxide 

• The effects of acid rain can be reduced by decreasing the amount of oxides of nitrogen and sulfur dioxide that are produced

• Catalytic convertors in vehicles can be used to remove oxides of nitrogen

• Emissions of sulfur dioxide can be reduced by either:

  • Using fuels which contain low levels of sulfur

  • Flue gas desulfurisation - this involves reacting the sulfur dioxide emitted from burning fuels containing sulfur, with calcium oxide therefore removing it from the flue gas

Oxides of Nitrogen in Car Engines

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Oxides of nitrogen

• These compounds (NO and NO₂) are formed when nitrogen and oxygen react in the high pressure and temperature conditions of internal combustion engines and blast furnaces

• Exhaust gases also contain unburned hydrocarbons and carbon monoxide

• Cars are fitted with catalytic converters which form a part of their exhaust systems

• Their function is to render these exhaust gases harmless

Catalytic converters

• They contain a series of transition metal catalysts including platinum and rhodium

• The metal catalysts are in a honeycomb within the converter to increase the surface area available for reaction

• A series of redox reactions occurs which neutralises the pollutant gases

• Carbon monoxide is oxidised to carbon dioxide:

2CO + O₂ → 2CO₂

• Oxides of nitrogen are reduced to N₂ gas:

2NO → N₂ + O₂

2NO₂ → N₂ + 2O₂

• A single reaction can summarise the reaction of nitrogen monoxide and carbon monoxide within a catalytic convertor:

2NO + 2CO → N₂ + 2CO₂

Catalytic converters are designed to reduce the polluting gases produced in car exhausts

• Unburned hydrocarbons can also be oxidised to carbon dioxide and water:

C₈H₁₈ + 12½O₂ → 8CO₂ + 9H₂O