Ammonia is synthesized industrially by the reaction N (g) + 3 H (g) → 2 NH (g)

CHEMISTRY · Multi-part · A Level · Chemistry · Thermodynamics · Thermodynamics

Problem

Ammonia is synthesized industrially by the reaction N2_2(g) + 3 H2_2(g) → 2 NH3_3(g). At 25 ∘C25\,^{\circ}\text{C} the reaction enthalpy is ΔH=−92.4 kJ mol−1\Delta H = -92.4\,\text{kJ\,mol}^{-1} and the entropy change is ΔS=−198 J mol−1 K−1\Delta S = -198\,\text{J\,mol}^{-1}\,\text{K}^{-1}. Assume ΔH\Delta H and ΔS\Delta S are temperature-independent. (a) Calculate ΔG\Delta G for the reaction at 298 K298\,\text{K}. Include units in your answer. (b) State whether the reaction is thermodynamically favorable at this temperature and justify your answer based on the numerical value obtained in part (a). (c) The industrial Haber–Bosch process is carried out at temperatures in the range 700–900 K. Without performing additional numerical calculations, predict how the sign and magnitude of ΔG\Delta G at 800 K compare with those at 298 K, and explain your reasoning in terms of thermodynamic principles.

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