Oxides of nitrogen, written together as NOx, are pollutants from vehicle engines and power stations.Unlike sulfur dioxide, they do not come from impurities in the fuel. The nitrogen and oxygen both come from the air. Nitrogen is very unreactive because of its strong N≡N triple bond, but the very high temperature and the spark in an engine provide enough energy for it to react:
N2 + O2 → 2NO
Nitrogen monoxide, NO, is colourless. In the air it is oxidised to nitrogen dioxide, a brown, toxic gas:
2NO + O2 → 2NO2
Effects of NOx:Acid rain: nitrogen dioxide dissolves in water droplets with oxygen to form nitric acid.
4NO2 + O2 + 2H2O → 4HNO3
Photochemical smog: in sunlight, NO2 reacts with unburnt hydrocarbons and oxygen to form ground-level ozone and other irritants. This brown haze is common in large, sunny cities with heavy traffic.
Health: NO2 irritates the lungs and eyes and makes asthma worse.Worked example: how many moles of NO2 can form from 1 mol of N2? 1 mol N2 forms 2 mol NO, and 2 mol NO forms 2 mol NO2, so the answer is 2 mol.Because NOx depends on the temperature of combustion, not the fuel, it is removed from vehicle exhausts by catalytic converters (next lesson).
Nitrogen monoxide, NO, is colourless. In the air it is oxidised to nitrogen dioxide, a brown, toxic gas:
Effects of NOx:Acid rain: nitrogen dioxide dissolves in water droplets with oxygen to form nitric acid.
Photochemical smog: in sunlight, NO2 reacts with unburnt hydrocarbons and oxygen to form ground-level ozone and other irritants. This brown haze is common in large, sunny cities with heavy traffic.
Health: NO2 irritates the lungs and eyes and makes asthma worse.Worked example: how many moles of NO2 can form from 1 mol of N2? 1 mol N2 forms 2 mol NO, and 2 mol NO forms 2 mol NO2, so the answer is 2 mol.Because NOx depends on the temperature of combustion, not the fuel, it is removed from vehicle exhausts by catalytic converters (next lesson).