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JAMB Chemistry 1980 Question 49

Question 49

Chemical Equilibrium

The synthesis of sulphuric acid by the contact process employs the following equilibrium step as one of its stages: 2SO2(g) + O2 ⇌ 2SO3(g) -ΔH. Which of the following conditions promotes the backward reaction?

  1. A.Increased pressure and decreased temperature
  2. B.Increased pressure, increased temperature and the presence of a catalyst
  3. C.Decreased pressure, decreased concentration of oxygen and increased temperature
  4. D.Decreased pressure, increased concentration of oxygen and increased temperature
  5. E.Decreased pressure, decreased concentration of oxygen and decreased temperature.
Show the answer and explanation

Answer: C (Decreased pressure, decreased concentration of oxygen and increased temperature)

Explanation

The forward reaction is exothermic and reduces the moles of gas. The backward reaction is favoured by lower pressure, higher temperature and removing oxygen (a reactant).