CHM1202 Assignment 2014-15

NAME: _________________________ Reg No. ________________________
Instructions: Answer all questions in the spaces provided. The completed assignment should be submitted to one of the Course Lecturers or the Departmental Secretary no later than 15:00 h on Friday May 8, 2015. a. Ammonia is manufactured using the equation; N2 (g) + 3H2 (g) ↔ 2NH3 (g) i) Use the data provided to calculate the entropy change for this reaction at 700K [4]
At 700 K; S (N2) = 212 J/K.mol; S (H2) = 149 J/K.mol; S (NH3) = 245 J/K.mol

ii) Using ideas about disorder, explain whether the sign of your answer to part a (i) is as expected. [2]
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iii) At 700 K the enthalpy change for the formation of NH3 is -55.1 kJ/mol. What is the Gibb’s energy change of the reaction in a (i) at 700K? (Include a sign and units in your answer). [5]

b. Use your answer to part a (iii) to calculate the equilibrium constant Kc for the reaction at 700 K; hence or otherwise state whether reactants or products are favoured at equilibrium. [5]

c. A mixture of N2, H2 and NH3is at equilibrium. The total pressure of the system is 150 atm. The partial pressures of N2 and NH3 in the mixture are 21 atm and 36 atm respectively. i) Write an expression for the equilibrium constant Kp for the formation of ammonia in terms of partial pressures for this reaction. [3]

ii) Calculate a value for Kp at 700 K. (Include units in your answer). [4]

d. In the manufacture of ammonia, pressures between 100 atm and 250 atm are used. i) State TWO advantages of using pressures above 100 atm [2]

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ii) State ONE disadvantage of using pressures above 250 atm [1]

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e. The reaction of ammonia with nitric acid produces ammonium nitrate which is used as a fertilizer for crops. i) Is the solution of ammonium nitrate acidic, basic or neutral (use equations to support to your answer) [5]
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ii) A farmer utilizing hydroponics to grow lettuces has added 5kg of ammonium nitrate to a vessel containing 1000 L of water. What is the pH of the resulting solution? [9]
{Kb (NH3) = 1.8x10-5}