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For the exothermic reaction 2SO2(g) + O2(g) <-> 2SO3(g), with delta H = -198 kJ, the conditions that favour maximum yield of SO3 are

1. low temperature, high pressure
2. any value of T and P
3. low temperature and low pressure
4. high temperature and high pressure

Correct answer: low temperature, high pressure

Solution

Being exothermic, low temperature favours the forward reaction; since gas moles decrease (3 to 2), high pressure also shifts equilibrium toward SO3.

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