Inside the hot cylinder of a car engine, two gases from the air react together to form oxides of nitrogen. These oxides then pass out with the exhaust gases...
Question 1 Report
Inside the hot cylinder of a car engine, two gases from the air react together to form oxides of nitrogen. These oxides then pass out with the exhaust gases and pollute the air.
(a) Explain how oxides of nitrogen are formed inside a car engine. [2]
(b) Write a balanced symbol equation for the formation of nitrogen monoxide (NO) from the two gases in the air. [2]
(c) State two environmental problems caused by oxides of nitrogen. [2]
(d) When oxides of nitrogen dissolve in rain water they help to form one of the acids in acid rain. Name this acid. [1]
(e) Describe how a catalytic converter reduces the amount of oxides of nitrogen leaving the exhaust. [3]
Answer Details
This question is about how oxides of nitrogen form in a car engine and how they are removed.
(a) Oxides of nitrogen form because [2]: the very high temperature inside the engine [1] provides enough energy to make nitrogen and oxygen (both from the air drawn in) react together [1]. These two gases do not normally react, so the heat of combustion is what forces them to combine.
(b) The formation of nitrogen monoxide is:
N2 + O2 → 2NO
Award [1] for correct formulae and [1] for balancing (2 N and 2 O on each side).
(c) Any two environmental problems, [1] each (max [2]): causes acid rain; causes breathing / respiratory problems; forms photochemical smog; damages plants.
(d) When oxides of nitrogen dissolve in rain water they form nitric acid (HNO3) [1], one of the acids in acid rain.
(e) In a catalytic converter [3]: the exhaust gases pass over a catalyst (platinum) [1]; the oxides of nitrogen react with carbon monoxide [1]; this forms harmless nitrogen and carbon dioxide [1], as shown by 2CO + 2NO → N2 + 2CO2. So one harmful gas is used to destroy the other.
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