Fig. 1 shows a simplified section of a sulfuric acid factory. Sulfur dioxide gas and oxygen enter a converter containing a solid vanadium(V) oxide catalyst....
Question 1 Report
Fig. 1 shows a simplified section of a sulfuric acid factory. Sulfur dioxide gas and oxygen enter a converter containing a solid vanadium(V) oxide catalyst. The reversible reaction forms sulfur trioxide. The gases are then cooled before sulfur trioxide is absorbed to form acid. Engineers monitor the temperature because a large yield is needed, but gas must also leave the converter quickly enough for continuous production.
(a) Complete the balanced equation for the converter reaction.
2SO2(g) + O2(g) ⇆ ................. [2]
(b) Name the catalyst in the converter. [1]
(c) State the effect of using a catalyst on the rate of both the forward and reverse reactions. [2]
(d) Explain why high pressure would increase the equilibrium yield of sulfur trioxide. [3]
(e) Give one reason why an extremely high pressure is not used in this factory. [2]
(f) When the temperature is increased, predict the change in sulfur trioxide yield if the forward reaction is exothermic. [2]
(g) State why the gases are cooled before sulfur trioxide is removed from the equilibrium mixture. [2]
Answer Details
(a) The balanced converter equation is:
\[\mathrm{2SO_2(g)+O_2(g)\rightleftharpoons2SO_3(g)}\]
The product is \(\mathrm{2SO_3(g)}\). [2]
(b) The catalyst is vanadium(V) oxide, \(\mathrm{V_2O_5}\). [1]
(c) A catalyst increases the rate of the forward reaction [1] and the reverse reaction. [1] It does not favour either side. [2]
(d) There are three moles of gas on the left and two on the right. [1] Increasing pressure favours the side with fewer gas molecules. [1] The equilibrium therefore moves right, producing more \(\mathrm{SO_3}\). [1] [3]
(e) Extremely high pressure requires stronger equipment [1] and this is expensive. [1] Alternatively, compressing gases uses substantial energy and is expensive. [2]
(f) The sulfur trioxide yield decreases. [1] Heating favours the endothermic, reverse direction when the forward reaction is exothermic. [1] [2]
(g) Cooling allows sulfur trioxide to condense or be removed. [1] Removing it prevents the reverse reaction from replacing it, so more \(\mathrm{SO_3}\) forms. [1] [2]
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