Ammonia, NH3, is manufactured from nitrogen and hydrogen by the Haber process. N2(g) + 3H2(g) ⇌ 2NH3(g) ΔH = –92 kJ mol–1

1. (a)(i)Some bond energies are given. N=N = 944 kJ mol–1 H–H = 436 kJ mol–1 (i) Explain the meaning of the term bond energy.[2]
2. (a)(ii)(ii) Use the data to calculate a value for the N–H bond energy. You must show your working. N–H bond energy = .............................................. kJ mol–1[2]
3. (b)(i)The Haber process is usually carried out at a temperature of approximately 400°C in the presence of a catalyst. Changing the temperature affects both the rate of production of ammonia and the yield of ammonia. The Boltzmann distribution for a mixture of nitrogen and hydrogen at 400 °C is shown. Ea represents the activation energy for the reaction. [Figure 1.1: Boltzmann distribution graph] (i) Using the same axes, sketch a second curve to indicate the Boltzmann distribution at a higher temperature.[2]
4. (b)(ii)(ii) With reference to the Boltzmann distribution, state and explain the effect of increasing temperature on the rate of production of ammonia.[3]
5. (b)(iii)(iii) State and explain the effect of increasing temperature on the yield of ammonia. Use Le Chatelier's principle to explain your answer.[3]
6. (c)(i)At a pressure of 2.00 × 10⁷ Pa, 1.00 mol of nitrogen, N2(g), was mixed with 3.00 mol of hydrogen, H2(g). The final equilibrium mixture formed contained 0.300 mol of ammonia, NH3(g). (i) Calculate the amounts, in mol, of N2(g) and H2(g) in the equilibrium mixture. N2(g) = .............................................. mol H2(g) = .............................................. mol[2]
7. (c)(ii)(ii) Calculate the partial pressure of ammonia, pNH3, in the equilibrium mixture. Give your answer to three significant figures. pNH3 = .............................................. Pa[3]
8. (d)(i)In another equilibrium mixture the partial pressures are as shown. substance partial pressure/Pa N2(g) 2.20 × 10⁶ H2(g) 9.62 × 10⁵ NH3(g) 1.40 × 10⁴ (i) Write the expression for the equilibrium constant, Kp, for the production of ammonia from nitrogen and hydrogen. Kp =[1]
9. (d)(ii)(ii) Calculate the value of Kp for this reaction. State the units. Kp = .............................................. units = ..............................................[2]
10. (d)(iii)(iii) This reaction is repeated with the same starting amounts of nitrogen and hydrogen. The same temperature is used but the container has a smaller volume. State the effects, if any, of this change on the yield of ammonia and on the value of Kp. effect on yield of ammonia ........................................................................................................................ effect on value of Kp ....................................................................................................................................[2]

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