OCR A Jun 2011 Paper 5 Q2

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2 Nitric acid, HNO3, is manufactured in large quantities. The main use of nitric acid is in the manufacture of fertilisers. In its industrial preparation, nitric acid is produced in three main stages. Stage 1 Ammonia is heated with oxygen in the air to form nitrogen monoxide, NO. Stage 2 The hot nitrogen monoxide gas is then mixed with air and cooled under pressure. Nitrogen dioxide, NO2, forms in a reversible reaction. 2NO(g) + O2(g) 2NO2(g) H = 115 kJ mol1 Stage 3 The nitrogen dioxide is reacted with water in a series of reactions to form nitric acid, HNO3. The first of these reactions forms a mixture of nitric acid, HNO3, and nitrous acid, HNO2. (a) In Stage 2, explain why the equilibrium mixture is both cooled and put under pressure.[3] (b) Construct an equation for the reaction that takes place in Stage 1 the first reaction that takes place in Stage 3.Stage 1:Stage 3:[2]OCR 2011<br /> (c) An industrial chemist carries out some research into the NO/O2/NO2 equilibrium used in Stage 2 of the manufacture of nitric acid. The chemist mixes together 0.80 mol NO(g) and 0.70 mol of O2(g) in a container with a volume of 2.0 dm3. The chemist heats the mixture and allows it to stand at constant temperature to reach equilibrium. The container is kept under pressure so that the total volume is maintained at 2.0 dm3. At equilibrium, 75% of the NO has reacted. (i) Write an expression for Kc for this equilibrium. (ii) Calculate the equilibrium constant, Kc, including units, for this equilibrium. [1] Kc =units[5] [Total: 11] Turn overOCR 2011<br />

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