OCR A Jun 2012 Paper 2 Q4

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The uses of catalysts have great economic and environmental importance. For example, catalysts are used in ammonia production and in catalytic converters. 12 (a) Nitrogen and hydrogen react together in the production of ammonia, NH3. N2(g) + 3H2(g) 2NH3(g) H = 92 kJ mol1 The activation energy for the forward reaction, Ea, is +250 kJ mol1. (i) Complete the enthalpy profile diagram for this reaction between nitrogen and hydrogen. Include theproducts enthalpy change of reaction, H activation energy for the forward reaction, Ea. enthalpy N2(g) + 3H2(g) progress of reaction [3] (ii) What is the value of the enthalpy change of formation of ammonia? answer =kJ mol1 [1] (iii) The reaction between nitrogen and hydrogen can be catalysed. Suggest a possible value for the activation energy of the catalysed forward reaction. answer =kJ mol1 [1] (iv) What is the value of the activation energy for the uncatalysed reverse reaction (the decomposition of ammonia into nitrogen and hydrogen)? answer =kJ mol1 [1]OCR 2012<br />
 (b) In a catalytic converter, nitrogen monoxide reacts with carbon monoxide. 13 (i) Write the equation for this reaction.[1] (ii) Outline the stages that allow nitrogen monoxide and carbon monoxide to react in a catalytic converter.[3] (c) Scientists monitor pollutant gases in the atmosphere. (i) State two modern analytical techniques that scientists can use to monitor environmental pollution.[2] (ii) Explain why it is important to establish international cooperation to reduce pollution levels.[1]OCR 2012 Turn over<br />
 (d) In the stratosphere, nitrogen monoxide, NO, is linked with ozone depletion. 14 Complete the equations below that describe how NO contributes to ozone depletion. step 1 step 2 NO + O3+NO2 +NO +overall+2O2 [3] (e) Hess law can be used to calculate enthalpy changes of reaction. The equation for the reaction that gives the enthalpy change of formation, Hf, of N2O(g) is as follows. N2(g) + O2(g) N2O(g) (i) It is not possible to measure the enthalpy change of formation of N2O(g) directly. Suggest why it is not possible.[1] (ii) The data below can be used to calculate the enthalpy change of formation, Hf, of N2O(g). reaction enthalpy change of reaction / kJ mol1 C(s) + N2O(g) C(s) + O2(g) CO(g) + N2(g) CO(g) 193 111 Calculate Hf for N2O(g).OCR 2012 Hf =kJ mol1 [2] [Total: 19]<br />

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