Skills for Chemistry: Open-book Paper 2007
Outline how the main pollutants are formed in vehicle engines and the environmental problems they cause. Explain why different types of vehicle engines produce different exhaust emissions.
Nitrogen Oxide (NOx gasess) is formed when fuels are burnt. Traffic and cars are the biggest emitters of NOx in the United Kingdom. NOx is formed when air is heated above 800°C, where nitrogen and oxygen react. These temperatures are reached in lightening or in combustion processes. (i) At these high temperatures the oxygen will divide homolytically to make two separate radicals:
O2 --> O + O
Each radical then reacts in a catalytic cycle involving a nitrogen molecule and an oxygen molecule, which then forms nitrogen monoxide and oxygen radical:
O + N2 --> NO + O
N + O2 --> NO +O
As the nitrogen monoxide cools it reacts with the oxygen to form nitrogen monoxide:
2NO + O2 --> 2NO2
NOx can also be formed when impure nitrogen compounds are burnt. (ii)
A range of nitrogen oxides (NOx), such as nitrous oxide and nitrogen dioxide, which will form nitric acid or nitrous acid that will contribute to acid rain. NOx is formed by reaction of nitrogen and oxygen in the air so is pretty much unavoidable. It can be reduced by decreasing the time that combustion occurs for and this is why airplane jet engines have become shorter in length over the years - a shorter combustion path through the engine will produce less NOx.
A range of sulphur oxides (SOx), which will form sulphuric or sulphurous acid that will also contribute to acid rain. SOx are formed by reaction of sulphur in the fuel with oxygen in the air and can be avoided by using low-sulphur fuels. (iii)
Outline how the main pollutants are formed in vehicle engines and the environmental problems they cause. Explain why different types of vehicle engines produce different exhaust emissions.
Nitrogen Oxide (NOx gasess) is formed when fuels are burnt. Traffic and cars are the biggest emitters of NOx in the United Kingdom. NOx is formed when air is heated above 800°C, where nitrogen and oxygen react. These temperatures are reached in lightening or in combustion processes. (i) At these high temperatures the oxygen will divide homolytically to make two separate radicals:
O2 --> O + O
Each radical then reacts in a catalytic cycle involving a nitrogen molecule and an oxygen molecule, which then forms nitrogen monoxide and oxygen radical:
O + N2 --> NO + O
N + O2 --> NO +O
As the nitrogen monoxide cools it reacts with the oxygen to form nitrogen monoxide:
2NO + O2 --> 2NO2
NOx can also be formed when impure nitrogen compounds are burnt. (ii)
A range of nitrogen oxides (NOx), such as nitrous oxide and nitrogen dioxide, which will form nitric acid or nitrous acid that will contribute to acid rain. NOx is formed by reaction of nitrogen and oxygen in the air so is pretty much unavoidable. It can be reduced by decreasing the time that combustion occurs for and this is why airplane jet engines have become shorter in length over the years - a shorter combustion path through the engine will produce less NOx.
A range of sulphur oxides (SOx), which will form sulphuric or sulphurous acid that will also contribute to acid rain. SOx are formed by reaction of sulphur in the fuel with oxygen in the air and can be avoided by using low-sulphur fuels. (iii)
