OCR A AS Jun 2016 Paper 2 Q4

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4 Nitrogen forms several different oxides. 10 N2O is a useful anaesthetic and NO has been linked to the depletion of ozone in the stratosphere. (a) The standard enthalpy changes of formation of N2O and NO are given in the table. Compound fH/ kJ mol1 N2O (g) NO (g) + 82.0 + 90.2 (i) Explain, in terms of bond breaking and bond making, why the enthalpy change of formation of NO is endothermic.[1] (ii) Draw a fully labelled enthalpy profile diagram to represent the enthalpy change of formation of N2O. The formulae, with state symbols, of the reactants and products should be included as part of the diagram. You are not expected to show the activation energy for the reaction. enthalpyOCR 2016 progress of reaction [2]<br /> 11 (b) N2O is supplied as a compressed gas in steel cylinders for use as an anaesthetic. The cylinders are stored at 20.0 C. Calculate the gas pressure, in Pa, in a 2.32 dm3 steel cylinder containing 187 g of N2O gas. Give your answer in standard form to three significant figures. pressure =Pa [4] (c) NO radicals catalyse the breakdown of ozone in the stratosphere. Write two equations to show how NO radicals catalyse this breakdown.[2]OCR 2016 Turn over<br />

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