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Reversible reactions and equilibria

Reversible reactions and equilibria

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Question 6

The flow diagram shows how sulfuric acid is manufactured from raw materials in the Contact process:

Sulfur, Air, Water→Sulfur dioxide→Sulfur trioxide→Oleum→Sulfuric acid \text{Sulfur, Air, Water} \rightarrow \text{Sulfur dioxide} \rightarrow \text{Sulfur trioxide} \rightarrow \text{Oleum} \rightarrow \text{Sulfuric acid} Sulfur, Air, Water→Sulfur dioxide→Sulfur trioxide→Oleum→Sulfuric acid

The sulfur dioxide needed can be formed by burning hydrogen sulfide gas in oxygen.

a.

Balance the equation for this reaction:

…H2S+…O2→…SO2+…H2O \dots\text{H}_2\text{S} + \dots\text{O}_2 \rightarrow \dots\text{SO}_2 + \dots\text{H}_2\text{O} …H2​S+…O2​→…SO2​+…H2​O
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b.

The equation for the catalytic oxidation of sulfur dioxide to sulfur trioxide (Reaction 2) is:

2SO2(g)+O2(g)⇌2SO3(g)ΔH=−197 kJ/mol 2\text{SO}_2\text{(g)} + \text{O}_2\text{(g)} \rightleftharpoons 2\text{SO}_3\text{(g)} \quad \Delta H = -197\text{ kJ/mol} 2SO2​(g)+O2​(g)⇌2SO3​(g)ΔH=−197 kJ/mol

Assuming that this reaction reaches equilibrium, explain what happens to the yield of sulfur trioxide if the reaction is carried out at a higher pressure but at the same temperature.

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c.

Assuming that this reaction reaches equilibrium, explain what happens to the yield of sulfur trioxide if the reaction is carried out at a higher temperature but at the same pressure.

[2]
d.

Reaction 2 can be represented on an energy profile. Explain how the energy level of the products compares to the reactants and how the enthalpy change (ΔH\Delta HΔH) is shown on an energy profile diagram for this reaction.

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e.

Reaction 2 is carried out using a vanadium(V) oxide catalyst. State the effect, if any, of using a catalyst on the enthalpy change for the reaction.

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f.

Explain how a catalyst increases the rate of a reaction.

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g.

The equations for some of the other reactions used in this manufacturing process are:

  • Reaction 3: S+O2→SO2\text{S} + \text{O}_2 \rightarrow \text{SO}_2S+O2​→SO2​
  • Reaction 4: 2SO2+O2⇌2SO32\text{SO}_2 + \text{O}_2 \rightleftharpoons 2\text{SO}_32SO2​+O2​⇌2SO3​
  • Reaction 5: SO3+H2SO4→H2S2O7\text{SO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{H}_2\text{S}_2\text{O}_7SO3​+H2​SO4​→H2​S2​O7​
  • Reaction 6: H2S2O7+H2O→2H2SO4\text{H}_2\text{S}_2\text{O}_7 + \text{H}_2\text{O} \rightarrow 2\text{H}_2\text{SO}_4H2​S2​O7​+H2​O→2H2​SO4​

Explain which two of these are redox reactions.

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h.

A manufacturer produces a batch of 160 kg160\text{ kg}160 kg of sulfur trioxide (SO3\text{SO}_3SO3​). Calculate the maximum mass of sulfuric acid (H2SO4\text{H}_2\text{SO}_4H2​SO4​) that can be made from this mass of sulfur trioxide, using the overall reaction:

SO3+H2O→H2SO4 \text{SO}_3 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_4 SO3​+H2​O→H2​SO4​

(Relative atomic masses: H=1\text{H} = 1H=1, O=16\text{O} = 16O=16, S=32\text{S} = 32S=32). Give a unit for your answer.

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Markscheme

Reversible reactions and equilibria Questions

  1. IGCSE
  2. /Chemistry
  3. /Reversible reactions and equilibria

28 exam-style questions on Edexcel IGCSE Chemistry Reversible reactions and equilibria. Each one has a worked solution and a mark scheme showing where the marks go.

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