The reversible reaction 2 SO2 (g) + O2 (g) <-> 2 SO3 (g) has a delta H value of -197 kJ/mol. Use Le Chatelier's principle to explain what conditions would give the highest equilibrium yield and why industry uses different conditions. (5 marks)

Le Chatelier's principle states that if a system is disturbed - something changes - the system will tend to move in the direction that minimises the change.  3 marks from: The forward reaction is exothermic (1)- the delta H is negative meaning that it gives out heat The equilibrium position will shift to the right at low temperatures (1)- to minimise the change as heat will be released  There are 3 moles of gas on the left and only 2 moles of gas on the right (1) - higher pressures favour fewer moles of gas as less space is taken up and so the pressure is lowered. The equilibrium position will shift to the right at high pressures (1) 2 marks from: Industry will use different conditions because high temperatures are needed to give a higher rate of reaction (1) - which means more product is generated in less time. High pressures are both expensive (1) and dangerous to maintain (1)