Question

In the formation of SO3 by contact process, the conditions used are-
A. Catalyst, optimum temperature, and higher concentration of reactants
B. Catalyst, optimum temperature, and lower concentration of reactants
C. Catalyst, high temperature and higher concentration of reactants
D. Catalyst, low temperature and lower concentration of reactants

Answer 1

Hint:When an external factor like temperature, pressure, or concentration is changed i.e, increased or decreased. The system tries to shift the equilibrium in such a way that the effect of these factors can be reduced. That means if to minimize the effect reaction needs to proceed forward it will favour the forward reaction and if to minimize the effect the reaction needs to proceed backward it will favour the backward reaction.

Complete answer:A chemical reaction in which the formation of the product and as well as the formation of reactant take place such type of reaction is called a reversible reaction. And reversible reactions try to attain chemical equilibrium. Equilibrium is a state where the rate of formation of a product is equal to the rate of formation of reactant.
The contact process is generally used for the formation of sulphuric acid. But this process can also be used for the formation of SO2, and SO3. This process is dependent on factors like temperature, pressure, and concentration.
The starting reactant of this reaction can be Sulphur S and Oxygen (air) O2, the burning of sulfur in presence of air. Or we can burn sulfide ores like pyrite (FeS2) with Oxygen (air) O2 both the reaction will give SO2.
(i) S_{(s)}+O_{2\ (g)}\longrightarrowSO_{2\ (g)}
(ii) 4FeS_{2\ (s)}+11O_{2\ (g)}\longrightarrow2{\rm Fe}_2O_{3\ (s)}+8SO_{2\ (g)}
Now conversion of SO2 in SO3
2SO_{2\ (g)}+O_{2\ (g)}\rlhar2SO_{3\ (g)} ΔH = -196 kJ mol-1
Conversion of SO2 into SO3 is a reversible process. The process of formation of SO3 is an exothermic process. Hence, we require a specific amount of temperature just to burn sulphur dioxide in presence of air to convert it into sulphur trioxide. V2O5 is used as a catalyst in the reaction. A higher concentration of SO2 and O2 will shift the reaction forward.
Thus, for the formation of SO3 by contact process the conditions required are the catalyst, optimum temperature, and higher concentration of reactants.

Thus, Option (A) is correct

Note: At higher temperatures since the conversion of sulphur trioxide into sulphur dioxide and oxygen is an endothermic process. At higher temperatures, the rate of this reaction will increase. Hence, the concentration of sulphur dioxide will increase and the concentration of sulphur trioxide will decrease.