OCR A Jun 2014 Paper 5 Q3

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3 Ethyne gas, C2H2, is manufactured in large quantities for a variety of uses. Much of this ethyne is manufactured from methane as shown in the equation below. 2CH4(g) C2H2(g) + 3H2(g) H = +377 kJ mol1 (a) Write an expression for Kc for this equilibrium. (b) A research chemist investigates how to improve the synthesis of ethyne from methane at a high temperature. [1]The chemist adds CH4 to a 4.00 dm3 container. The chemist heats the container and allows equilibrium to be reached at constant temperature. The total gas volume does not change. The equilibrium mixture contains 9.36102 mol CH4 and 0.168 mol C2H2. (i) Calculate the amount, in mol, of H2 in the equilibrium mixture. amount of H2 =mol [1] (ii) Calculate the equilibrium constant, Kc, at this temperature, including units. Give your answer to three significant figures. Kc =units [3]OCR 2014<br /> (iii) Calculate the amount, in mol, of CH4 that the chemist originally added to the container. amount of CH4 =mol [1] (c) The chemist repeats the experiment three times. In each experiment the chemist makes one change but uses the same initial amount of CH4. Complete the table to show the predicted effect of each change compared with the original experiment. Only use the words greater, smaller or same. Change Kc Equilibrium amount of C2H2(g) / mol Initial rate The container is heated at constant pressure A smaller container is used A catalyst is added to CH4 at the start [3] (d) In this manufacture of ethyne, hydrogen is also produced. To improve the atom economy of the process, it is important to make use of the hydrogen. For example, hydrogen can be used in the extraction of some metals from their ores. State two other large-scale uses of the hydrogen. 12[1] [Total: 10]OCR 2014 Turn over<br />

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