Question

When Sulphur is burnt in air, the major product is Sulphur trioxide – True or False?

• A. True
• B. False

Answer 1

The correct option is B False

It is interesting to note that the formation of sulphur trioxide is thermodynamically more favored than that of sulphur dioxide.

For example, the heats of formation ${\Delta }_f{H}^{\circ }forS{O}_{3}is-370kJ.mo{l}^{-1}$ while that for $S{O}_2$ is only $-300kJ.mo{l}^{-1}$.

Despite this, the oxidation of Sulphur almost always yields $S{O}_2$ than $S{O}_3$ because the oxidation to the Sulphur trioxide has a significantly higher activation energy. Hence, the pathway from sulphur dioxide to sulphur trioxide is controlled kinetically:

$2S{O}_2\left(g\right)+O_2\left(g\right)\stackrel{Pt,\Delta }{⟶}2S{O}_3\left(g\right)$

In the contact process for the manufacture of Sulphuric acid, $V_2{O}_5$ is the preferred catalyst for the above reaction. Earlier, platinized asbestos was used.