Industrial Chemistry and Environmental Pollution — A/L Chemistry

How do I practise Industrial Chemistry and Environmental Pollution?

1 question with a worked solution

Check before you answer: Optimal Industrial Conditions: Justifying compromised temperature and pressure choices (e.g., Haber process: 450 °C, 200 atm, Fe catalyst) balancing thermodynamic equilibrium yield against kinetic reaction rate.

1. In the industrial Contact Process for the manufacture of sulfuric acid, sulfur dioxide is converted to sulfur trioxide via the reversible exothermic reaction: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) (ΔH = -196 kJ mol⁻¹). Why is an operating temperature of approximately 450 °C utilized rather than a much higher or much lower temperature?
   1. A) Higher temperatures shift the equilibrium toward sulfur trioxide but cause dangerous high-pressure explosions
   2. B) 450 °C is an optimum compromise: lower temperatures favor equilibrium yield but have unacceptably slow reaction rates, while higher temperatures shift equilibrium to the left
   3. C) 450 °C is the exact boiling point of sulfur trioxide, enabling continuous condensation
   4. D) Higher temperatures decompose the vanadium(V) oxide catalyst into inactive vanadium(II) oxide
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   Correct answer: B) 450 °C is an optimum compromise: lower temperatures favor equilibrium yield but have unacceptably slow reaction rates, while higher temperatures shift equilibrium to the left

   Because the forward reaction is exothermic (ΔH < 0), by Le Chatelier's principle, lower temperatures shift the equilibrium to the right, producing a higher percentage yield of SO₃. However, at low temperatures, the kinetic reaction rate is too slow for commercial viability, even with a V₂O₅ catalyst. At higher temperatures, the reaction proceeds rapidly but the equilibrium shifts left, significantly reducing the yield. An intermediate temperature of ~450 °C is an optimum compromise providing an economic reaction rate with ~98% conversion efficiency.

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   Step 1: State thermodynamic equilibrium considerations: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) is exothermic (ΔH = -196 kJ mol⁻¹). According to Le Chatelier's principle, decreasing temperature favors the forward exothermic reaction (increases K_p and equilibrium conversion). Step 2: State kinetic reaction rate considerations: According to collision theory, lower temperatures decrease the fraction of reactant molecules possessing energy ≥ activation energy E_a, making the rate too slow for an industrial plant. Step 3: Analyze role of V₂O₅ catalyst: Vanadium(V) oxide requires a minimum operating temperature of ~400–450 °C to become catalytically active. Step 4: Conclude on the compromise: 450 °C provides an optimum balance where rate is sufficiently fast and multi-stage beds achieve >98% conversion. Answer: 450 °C is an optimum compromise: lower temperatures favor equilibrium yield but have unacceptably slow reaction rates, while higher temperatures shift equilibrium to the left.
   Modelled on: the A/L Chemistry examination pattern

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Where does Industrial Chemistry and Environmental Pollution fit in the syllabus?

Grade 13 · Term 3