6.2.5 - Combustion & Air Pollution

• pollutants

  carbon monoxide

  Oxides of nitrogen and sulfur

  carbon particulates

  unburned hydrocarbons
• how are pollutants formed?

  during combustion of alkane fuels
• why engines that burn fuds can pollute the air

  they don't burn fuel completely

  the feel contains impurities

  run at high temperatures so nitrogen & oxygen in air react
• when does incomplete combustion happen?

  when there's a limited supply of oxygen so some atoms in the fuel aren't fully oxidised

  produces carbon, carbon monoxide & water
• problem with carbon monoxide

  toxic, colourless, odourless gas that forms strong bonds with haemoglobin in the blood preventing oxygen from binding to it leading to oxygen deprivation which can be fatal
• problem with carbon/soot

  particles can enter deep into the lungs causing coughing & headache in short term and in long term, heart disease or lung cancer
• what does impurities of sulfur in fuels produce?

  sulfur dioxide when burnt which damages catalysts in catalytic converter f is acidic so dissolves in atmospheric water forming sulfuric acid leading to acid rain
• acid rain

  hills fish in lakes

  damages buildings & statues

  destroys vegetation
• how is sulfur removed from crude oil?

  crude oil is mixed with hydrogen and passed over a hot catalyst producing a hydrocarbon and hydrogen sulfide

  hydrogen sulfide is oxidised to sulfur in 2 stages
• how are oxides of nitrogen produced

  high temperature & pressure in a car engine provides enough energy for nitrogen and oxygen to react
• problem with oxides of nitrogen

  in sunshine NO2 breaks into NO and oxygen radicals which combine with oxygen molecules to form ozone that can mix with unburned hydrocarbons forming a mixture of irritant chemicals that under no mind builds up to photochemical smog
• what do catalytic converters do?

  remove pollutants that would be released from car exhausts
• how do catalytic converters remove pollutants?

  in the presence of a catalyst carbon monoxide & unburned hydrocarbons react with nitrogen oxides to form carbon dioxide and water

  redox reaction
• structure of catalytic converters

  ceramic honeycomb shape coated with a thin layer of metals like rhodium, platinum or palladium which gives a large surface area so increases rate of reaction