Sulfuric acid

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C8.09 The manufacture of sulfuric acid
The raw materials for making sulfuric acid are sulfur and air.  Sulfur is obtained by heating sulfide ores e.g. FeS in air or from natural deposits.  The are a number of stages.
Stage (a) molten sulfur is burned in air to form sulfur dioxide
S(l) + O₂(g) ---> SO₂(g)
Stage (b) sulfur dioxide is passed over a catalyst of vanadium pentoxide at a temperature of about 450^oC and a pressure of about 2 atmospheres.  Sulfur trioxide is formed in an equilibrium reaction.
SO₂(g) + O₂(g) <---> SO₃(g)
Stage (c) Sulfur trioxide is passed up through a flow of 98% sulfuric acid and is absorbed.  This last stage is a less exothermic way of reacting sulfur trioxide with water.
SO₃(g) + H₂O(l) ---> H₂SO₄(l)
Task C8.09

C8.10 Operating conditions used in the Contact process (high tier)
Temperature
The reaction below is exothermic, energy given out when sulfur trioxide forms, but energy is taken in if sulfur trioxide breaks up.
SO₂(g) + O₂(g) <---> SO₃(g)  ;  DH = - 197kJ/mol
Reactions resist changes (le Chatelier's principle).
If the temperature goes up the reaction tries to prevent this by taking in energy.
The reaction can take energy by breaking up sulfur trioxide. 
So if the temperature increases then sulfur trioxide breaks up.
The position of equilibrium moves to the left.
When the temperature falls the position of the equilibrium moves to the right so more sulfur trioxide is formed .  A low temperature is best for a high yield.
At low temperature the rate is low so a compromise of about 450^oC is used.
Catalyst
As the rate is low at the optimum temperature a catalyst is used to increase the rate.  The vanadium pentoxide is used.
Pressure
On the left hand side of the equation there are 2 molecules/2 mol of gas/2 volumes of gas
On the right hand side there is only 1 molecules/1mol of gas/1 volumes of gas.
Pressure is reduced if the position of the equilibrium moves to the right, so an increase in pressure causes a shift to the right so more sulfur trioxide is formed.  As high pressure favours a big yield so 2 atmospheres pressure is used.  This is not very high as even at this pressure the yield is high at about 95%.
Task C8.10  You as the chemical engineer are asked by one manager to run your sulfuric acid plant at 600^oC to make acid faster and by another manager to run it at 300^oC to save money on heating.  Write a response to each of these suggestions using your chemistry knowledge.

C8.11 Uses of sulfuric acid