Rate expression for ammonia synthesis is___________________?
Correct answer: D. Kc=4x2v2/(a-x)(b-3x)3
- A. Kc=x2/(a-x)(b-x)
- B. Kc=x2/v(a-x)
- C. Kc=4×2/(a-2x)2(b-x)
- D. Kc=4x2v2/(a-x)(b-3x)3
Explanation
For N2 + 3H2 ⇌ 2NH3, if the initial amounts are a mol of N2 and b mol of H2, and x mol of N2 reacts in a vessel of volume v dm3, the equilibrium concentrations are (a-x)/v mol dm-3, (b-3x)/v mol dm-3, and 2x/v mol dm-3. Hence Kc = (2x/v)^2 / [((a-x)/v)((b-3x)/v)^3] = 4x^2v^2/((a-x)(b-3x)^3). The likely trap is option a, which ignores the 3:1 hydrogen-to-nitrogen ratio and the volume factors.
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About Haber's Process
Haber's process produces ammonia by reacting nitrogen with hydrogen in a reversible, exothermic equilibrium. The topic covers the iron catalyst, operating temperature and pressure, Le Chatelier's principle, the compromise between reaction rate and equilibrium yield, and the removal and recycling of ammonia and unreacted gases.
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