OCR A Jun 2011 Paper 2 Q3

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3 Nitrogen monoxide is an atmospheric pollutant, formed inside car engines by the reaction between nitrogen and oxygen. N2(g) + O2(g) 2NO(g) H = +66 kJ mol1 This reaction is endothermic. (a) (i) Explain the meaning of the term endothermic.[1] (ii) What is the value for the enthalpy change of formation of nitrogen monoxide? (b) (i) Complete the enthalpy profile diagram for the reaction between nitrogen and oxygen. answer =kJ mol1 [1] On your diagramadd the product label the activation energy as Ea label the enthalpy change as H. enthalpy N2(g) + O2(g) reaction pathway [3] (ii) Explain the meaning of the term activation energy.[1]OCR 2011 Turn over<br />
 (c) A research chemist investigates the reaction between nitrogen and oxygen. She mixes nitrogen and oxygen gases in a sealed container. She then heats the container at a constant temperature for one day until the gases reach a dynamic equilibrium. (i) Explain, in terms of the rate of the forward reaction and the rate of the backward reaction, how the mixture of N2(g) and O2(g) reaches a dynamic equilibrium containing N2(g), O2(g) and NO(g).[2] (ii) The research chemist repeats the experiment at the same temperature using the same initial amounts of N2(g) and O2(g). This time she carries out the experiment at a much higher pressure. Suggest whymuch less time is needed to reach dynamic equilibriumthe composition of the equilibrium mixture is the same as in the first experiment.[5] (iii) The reaction between nitrogen and oxygen in a car engine does not reach a dynamic equilibrium. Suggest why not.[1]OCR 2011<br />
 (d) Nitrogen monoxide is a radical. What does this tell you about a molecule of nitrogen monoxide?[1] (e) Oxides of nitrogen, NOx, are atmospheric pollutants. (i) Nitrogen monoxide reacts with oxygen to form NO2. Write an equation for the formation of NO2 from nitrogen monoxide and oxygen.[1] (ii) Aeroplane engines produce nitrogen monoxide. Describe, with the aid of equations, how nitrogen monoxide catalyses ozone depletion in the stratosphere.[3] (iii) Outline the use of infrared spectroscopy in identifying air pollutants such as NOx.[2] [Total: 21]OCR 2011 Turn over<br />

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