OCR A Jun 2013 Paper 2 Q5

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5 Nitrogen forms several oxides including N2O4, N2O and NO. 12 (a) A rocket uses the reaction between N2O4 and methylhydrazine, CH3NHNH2, equation 5.1, to release a large amount of energy. 4CH3NHNH2(l) + 5N2O4(l) 4CO2(g) + 12H2O(g) + 9N2(g) equation 5.1 Some enthalpy changes of formation, Hf, are shown in the table. Substance CH3NHNH2(l) N2O4(l) CO2(g) H2O(g) Hf / kJ mol1 +54 20 394 242 Using the enthalpy changes of formation, Hf, calculate the enthalpy change of reaction in equation 5.1. enthalpy change of reaction =kJ mol1 [3]OCR 2013<br /> 13 (b) Under certain conditions nitrogen reacts with oxygen to make N2O. 2N2(g) + O2(g) 2N2O(g) equation 5.2 The enthalpy profile diagram for this reaction is shown in Fig. 5.3. enthalpy 2N2(g) + O2(g) 2N2O(g) +447 kJ mol1 +164 kJ mol1 progress of reaction Fig. 5.3 (i) Calculate the enthalpy change when 240 dm3 of N2O(g), measured at room temperature and pressure, is formed from N2 and O2. enthalpy change =kJ [2] (ii) What is the enthalpy change of formation, Hf, of N2O(g)? Hf =kJ mol1 [1]OCR 2013 Turn over<br /> 14 enthalpy 2N2(g) + O2(g) 2N2O(g) +447 kJ mol1 +164 kJ mol1 progress of reaction Fig. 5.3 (repeated) (iii) The reaction in equation 5.2 is reversible. 2N2(g) + O2(g) 2N2O(g) equation 5.2 Calculate the activation energy, Ea, for the reverse reaction. Ea (reverse reaction) =kJ mol1 [1] (c) Describe and explain, using equations, how the concentration of ozone in the stratosphere is maintained.[2] (d) In the stratosphere, NO catalyses the breakdown of ozone. Write two equations to show how NO catalyses this breakdown.[2]OCR 2013 [Total: 11]<br />

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