A) It is called the contact process because the reacting gases, sulphur(IV) oxide and oxygen, come into contact with the solid catalyst (vanadium(V) oxide) on its surface.

a) It is called the contact process because the reacting gases, sulphur(IV) oxide and oxygen, come into contact with the solid catalyst (vanadium(V) oxide) on its surface.

b) The catalyst used is vanadium(V) oxide ($\text{V}_2\text{O}_5$).

c) The balanced chemical equation for the basic reaction is:

$$2\text{SO}_2(g) + \text{O}_2(g) \xrightarrow{\text{V}_2\text{O}_5} 2\text{SO}_3(g)$$

d) Two other conditions necessary are:
Condition I: High temperature (approximately $450^\circ\text{C}$)
Condition II: Moderate pressure (approximately 1-2 atmospheres)

e) One large scale use of sulphuric (VI) acid is in the manufacture of fertilizers (e.g., ammonium sulfate).

15.

a) The process that takes place is deliquescence.

b) One use of the process displayed by anhydrous calcium chloride is as a drying agent (desiccant) to remove moisture from gases or liquids.