Edexcel Jan 2010 Paper 4 Q24

Answers available below

PMT 24 Hydrogen is used in very large quantities as a fuel, as a reducing agent, and in the production of ammonia. Hydrogen is manufactured by steam reforming of methane from natural gas. Two reactions are involved, both being in equilibrium in closed systems. Reaction I CH4(g) + H2O(g) (cid:85) CO(g) + 3H2(g) H = + 210 kJ mol1 Reaction II CO(g) + H2O(g) (cid:85) CO2(g) + H2(g) H = 42 kJ mol1 (a) Write the expression for the equilibrium constant, Kp, for reaction I. (1) (b) Reaction I occurs at a temperature of 1000 K and a pressure of 30 atm over a nickel catalyst. (i) State and explain the effect, if any, on the value of Kp of increasing the pressure on the reaction. (1)(ii) Explain, in terms of your answers to (a) and (b)(i), why an increase in the pressure leads to a decrease in yield in reaction I. (2)18 *N36289A01828*<br /> PMT (iii) Increasing the pressure on this heterogeneously-catalysed reaction I has very little effect on the rate of the reaction. Suggest why this is so. (2)(c) The expression for Kp for reaction II is P P H CO P P CO H O At a particular temperature and 30 atm pressure, a mixture of equal amounts of carbon monoxide and steam react to give an equilibrium mixture where 75 % of the CO has reacted. Calculate the value of Kp showing your working. (3) *N36289A01928* 19 Turn over<br /> (d) Carbon dioxide and hydrogen are separated by washing the gas with potassium carbonate solution to give potassium hydrogencarbonate solution, leaving hydrogen in the gas stream. Potassium carbonate is expensive and is regenerated by heating the potassium hydrogencarbonate and liberating the carbon dioxide. (i) Hydrogen is often claimed to be a non-polluting fuel as it only produces water on burning. Explain why its manufacture using reactions I and II does not support this claim.(ii) Write the equation for the thermal decomposition of potassium hydrogencarbonate. State symbols are not required. PMT (1) (1) (1) (e) Although industrial processes are often discussed in terms of equilibria, they are rarely allowed to reach equilibrium. Suggest why, apart from insufficient reaction time, this is so.(Total for Question 24 = 12 marks) TOTAL FOR SECTION B = 50 MARKS 20 *N36289A02028*<br />

Show answer