Sulfuric acid is manufactured by the Contact process. One stage in this process is the conversion of sulfur dioxide into sulfur trioxide in the presence of a heterogeneous catalyst of vanadium(V) oxide, V2O5. 2O=S=O(g) + O=O(g) ⇌ 2O=S=O(g) ΔΗ = –196 kJ mol⁻¹

1. (a)(i)State the effect of a catalyst on a reaction. Explain how a catalyst causes this effect.[2]
2. (a)(ii)State the meaning of the term heterogeneous as applied to catalysts.[1]
3. (b)Some bond energies are given. bond | bond energy/kJmol⁻¹ --- | --- S=O (in SO₂) | 534 O=O | 496 Use the data, and the enthalpy change for the conversion of sulfur dioxide into sulfur trioxide, to calculate a value for the S=O bond energy in SO3. S=O bond energy in SO3 =[2]
4. (c)The Contact process is usually carried out at a temperature of about 400°C and a pressure just above atmospheric pressure. Using a higher or lower temperature and pressure would affect both the rate of production of sulfur trioxide and the yield of sulfur trioxide. A reaction pathway diagram for both the catalysed and uncatalysed reactions between SO2 and O₂ is shown. [Figure: Reaction pathway diagram with energy changes A-E labeled, showing catalysed and uncatalysed pathways for 2SO2 + O2 → 2SO3] The letters A–E represent energy changes. Complete the table by stating which letter, A-E, represents the energy change described. energy change | letter --- | --- the energy change for the production of SO3 | the activation energy for the production of SO3 in the absence of a catalyst | the activation energy for the first step in the decomposition of SO3 in the presence of a catalyst | [3]
5. (d)(i)The equation for this stage of the Contact Process is shown. 2SO2(g) + O2(g) ⇌ 2SO3(g) ΔΗ = –196 kJ mol⁻¹ State and explain the effect of increasing temperature on the rate of production of SO3.[3]
6. (d)(ii)State and explain the effect of increasing temperature on the yield of SO3.[3]
7. (e)The SO3 produced is converted to sulfuric acid in two stages. In the first stage the SO3 is reacted with concentrated sulfuric acid to produce oleum, H2S2O7. The oleum is then reacted with water to form sulfuric acid. Suggest an equation for the reaction of oleum, H2S2O7, with water to form sulfuric acid.[1]
8. (f)(i)SO2 reacts with water to form sulfurous acid. Sulfurous acid is a weak Brønsted-Lowry acid, while sulfuric acid is a strong Brønsted-Lowry acid. Complete the 'dot-and-cross' diagram to show the bonding in a molecule of SO2. Show outer electrons only. [Figure: Incomplete dot-and-cross diagram for SO2 molecule][1]
9. (f)(ii)State the meaning of the term strong Brønsted-Lowry acid.[2]
10. (f)(iii)Write an equation to show the acid-base behaviour of sulfuric acid with water. Include state symbols.[2]

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