OCR A Jun 2010 Paper 2 Q6 (with explained solutions) |

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OCR A Jun 2010 Paper 2 Q6

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21 6 An important reaction in the manufacture of nitric acid is the catalytic oxidation of ammonia. 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g) H =909 kJ mol1 (a) Low pressures and low temperatures would give the maximum equilibrium yield of NO. Explain why.[2] (b) The actual conditions used in the catalytic oxidation of ammonia include 900 C and an increase in pressure. Suggest why these conditions are a compromise.[3] (c) A factory makes 2.50105 mol of NO a day. (i) How much energy is released every day? energy released = . kJ [1] (ii) Suggest how this energy can be used to reduce the cost of making NO.[1]OCR 2010 [Total: 7] Turn over<br />

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F322 Question ii Mark Scheme June 2010 Additional Guidance ALLOW low pressure because more (gas) moles on right hand side of equation ANNOTATE WITH TICKS AND CROSSES ALLOW pushes gases through system ALLOW two or more significant figures Calculator answer is 5.6812500107 ALLOW used to heat rest of factory OR sold to the national grid Provide energy to create conditions is not sufficient because one condition is pressure Expected Answers Low pressure because more (gas) molecules on right hand side of equation OR low pressure because V = positive (cid:57) Low temperature because the (forward) reaction is exothermic (cid:57) Marks Increased pressure speeds up reaction / ora (cid:57) 900 oC increases the rate OR increased temperature speeds up reaction / ora (cid:57) Idea that high enough temperature without compromising yield OR idea that high enough pressure without compromising yield (cid:57) 5.68107 / 5.7107 (cid:57) Used to heat the incoming gases (cid:57) Total 19<br />

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