OCR A Jan 2013 Paper 2 Q2

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2 Phosphoric acid, H3PO4, can be manufactured by a two step process involving the reaction of phosphorus with oxygen, followed by a reaction with water. P4(s) + 5O2(g) P4O10(s) H1 = 2984 kJ mol1 P4O10(s) + 6H2O(l) 4H3PO4(l) H2 (a) Explain why H1 represents the enthalpy change of formation of P4O10.[2] (b) Enthalpy changes of formation are shown in the table below. Substance Enthalpy change of formation, Hf / kJ mol1 P4O10(s) H2O(l) H3PO4(l) 2984 286 1267 Calculate the enthalpy change of reaction, H2. H2 =kJ mol1 [3] (c) Write the overall equation for the manufacture of H3PO4 from P4. Use this equation to explain why this process has a 100% atom economy.[2]OCR 2013 [Total: 7] Turn over<br />

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