How does sulfuric acid form and how it is made?a brief summary

There are two main processes used in the production of
H2SO4, lead chamber process and contact
process. Lead  process chamber is an old method, and it produces a
solution of acid in water, of concentration 62-78%. Through the contact process,
sulfuric acid is obtained easily. In both processes, sulfur dioxide, SO2 is oxidized to
sulfur trioxide, SO3, which is dissolved in water.

Sulphur
dioxide is produced by burning of sulfur:

S (s) + O2 (g)
--> SO 2 (g)

by roasting pyrite (iron sulphide) or
other metal sulfides

4 Fes (s) + 7 O2 (g) --> 2
Fe2O3 (s) + 4 SO 2 (g)

or by burning hydrogen
sulphide

2 H2S (g) + 3 O2 (g) --> 2 SO2 (g) +2 H2O
(g)

Sulfur dioxide is catalytically oxidized to sulfur
trioxide

2SO2 (g) + O2 (g) --> 2 SO3
(g)

In the absence of catalyst, oxidation of SO2 is slow.
In the old lead chamber process, the catalyst is azot carbon dioxide. In contact
process, the catalyst is vanadium oxide, V2O5. Sulfur trioxide is dissolved in 98%
sulfuric acid, it is reacting with 2% water to form
H2SO4.

H2SO4

SO3 (g) + H2O (l)
--> H2SO4 (l)