12201 18 Sulfur dioxide is reacted with oxygen to form sulfur trioxide in the manufacture of sulfuric acid in the Contact Process. 2SO2(g)    +    O2(g)   ⇌    2SO3(g)    −197 kJ (a) State the pressure and catalyst used in this reaction. [2] (b) Explain why the temperature chosen for this reaction, 450 °C, can be described as a compromise temperature. [2] (c) Write an expression for Kc for the above reaction. [1] 12201 [Turn over (d) Sulfur dioxide, oxygen and sulfur trioxide were mixed and allowed to reach equilibrium in a 20 dm3 container. At equilibrium, 8.0 moles of sulfur dioxide and 10.0 moles of sulfur trioxide were present. Calculate the number of moles of oxygen present if the numerical value of Kc is 27.9 mol−1 dm3. [4]