What are the favorable conditions for maximum yield of Sulphur trioxide?

High pressure, low temperature, excess of oxygen

The correct answer is option 1. High pressure, low temperature, excess of oxygen.

The favorable conditions for the maximum yield of sulfur trioxide \((SO_3)\) in the industrial production process, specifically the Contact Process, are high pressure, low temperature, excess of oxygen

High Pressure: The reaction for the formation of sulfur trioxide from sulfur dioxide and oxygen is:

\( 2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g) \)

According to Le Chatelier's Principle, increasing the pressure shifts the equilibrium towards the side with fewer gas molecules. Since there are 3 moles of gas on the reactants' side (2 moles of \(SO_2\) and 1 mole of \(O_2\)) and 2 moles on the products' side (2 moles of SO3), high pressure favors the formation of \(SO_3\).

Low Temperature: The formation of sulfur trioxide is an exothermic reaction (releases heat):

\(2SO2(g) + O2(g) \rightarrow 2SO3(g) \quad \Delta H < 0\)

Again, according to Le Chatelier's Principle, decreasing the temperature shifts the equilibrium towards the exothermic direction (product side) to produce more heat, favoring the formation of SO3. However, the temperature cannot be too low because the reaction rate would become too slow. Industrially, an optimum temperature (around 400-450°C) is used to balance the rate and yield.

Excess of Oxygen: Using an excess of oxygen helps drive the reaction towards the production of sulfur trioxide. This is again based on Le Chatelier's Principle, where increasing the concentration of a reactant \((O_2)\) shifts the equilibrium towards the products.

In industrial practice, these conditions are carefully controlled to maximize the yield of \(SO_3\) while maintaining an economically viable rate of production. Catalysts like vanadium \((V)\) oxide \((V_2O_5)\) are also used to increase the reaction rate.