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Advanced subsidiary GCE Salters chemistry open book paper

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Introduction

Advanced subsidiary GCE Salters chemistry open book paper In the internal combustion engine, there are 4 primary pollutants released. These are; hydrocarbons, carbon dioxide, carbon monoxide and NOx compounds. Hydrocarbons are formed when there is uncombusted fuel remaining in the exhaust fumes. Carbon dioxide is produced as the carbon from the fuel ignites with a plentiful supply of oxygen. This allows complete combustion of the carbon. CO2 is believed to be contributing to global warming and is considered as a greenhouse gas. Carbon monoxide occurs due to incomplete combustion of carbon from the fuel. This occurs during a limited supply of oxygen. Carbon monoxide is a toxic gas that inhibits the ability of hemoglobin to carry oxygen. Nitrogen oxide compounds are formed by the reaction of nitrogen from the air reacting with oxygen from the air in the high temperatures of the engine (800�C+). ...read more.

Middle

This is because diesel engines use a different fuel to the conventional and lean burn engines. The table below shows the levels of pollutants: Atmospheric nitrogen can lead to the production of acid rain. NO emissions leave the exhaust and remain in the lower atmosphere where they are oxidized to NO2. 2NO + O2 --> 2NO2 Or... NO + O3 --> NO2 + O2. This NO2 can then react with OH radicals in the environment to form nitric acid which mixes with water vapour and returns to Earth as acid rain: NO2 + OH --> HNO3 Heterogenous catalysts are now used to reduce the levels of air pollution. These work by adsorbing the reactants onto the surface of the catalyst. This weakens the bonds between atoms and the molecules break. This allows new bonds to form between the reactants to form the products. ...read more.

Conclusion

3 Way catalytic converters are designed to prevent the emissions of dangerous chemicals, by removing them from the exhaust gasses. 3 way catalytic converters remove carbon monoxide, hydrocarbons and nitrogen oxides. To remove carbon monoxide, a reaction occurs between CO and oxygen which creates carbon dioxide. 2CO + O2 --> 2CO2 To remove unburnt hydrocarbons, a reaction with oxygen occurs, to produce water vapour and carbon dioxide. C7H16 + 11O2 --> 8H2O + 7CO2 To remove nitrogen oxides, a reaction with carbon monoxide occurs to produce carbon dioxide and nitrogen. 2CO + 2NO --> 2CO2 + N2 Under a "stoichiometric" fuel mixture, optimum conversion of the pollutants occurs. There is also compound called Ceria present on many catalytic converters, which improves the performance of the catalyst, by storing oxygen when the exhaust mixture is lean and releasing oxygen when the mixture is rich. This allows the oxidation of pollutants even when there is very little oxygen in the exhaust mixture. ...read more.

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