Question

In the reaction, $2S{ O }_{ 2 }(g)\quad +\quad { O }_{ 2 }\quad \rightleftharpoons \quad 2S{ O }_{ 3 }(g)\quad +\quad XCal$ most favourable conditions of temperature and pressure for greater yield of $S{O}_{3}$ are:
A.Low temperature and low pressure
B.High temperature and low pressure
C.High temperature and high pressure
D.Low temperature and high pressure

Answer 1

Hint: This reaction is basically an industrial process in the production of sulphuric acid. It should be performed at sufficient temperature and pressure conditions.
Complete step by step answer: The above reaction is an oxidation process. The oxidation of sulphur dioxide to sulphur trioxide takes place using oxygen. This reaction takes place on a catalyst of vanadium(V) oxide to speed up the reaction. It is an exothermic reaction.
The most favourable conditions for greater yield of $S{O}_{3}$ are low temperature and high pressure.
High pressure is needed because the no. of moles of the product is less than that of reactants.
$\delta {n}_{g} = 2 - (2+1) = -1$
$\delta {n}_{g} < 0$
According to Le Chatelier's principle, when a system at equilibrium is disturbed, the equilibrium tends to shift in a direction such that the effect of the change is nullified.
When the pressure is increased, the equilibrium will shift to the product side as it contains less number of moles of gaseous species. This compensates the effect of increase in pressure. Hence, more and more products will be formed.
Exothermic reaction is favoured by low temperatures. Heat is evolved in this reaction. Thus, low temperature is required.
Hence, the option (d) is the correct one.

Note: Sulphur trioxide is used in the manufacture of chemicals and explosives. It is used as a bleaching agent to remove residual hydrogen peroxide, or as a digesting agent.