5.27      describe the manufacture of sulfuric acid by the contact process, including the essential conditions:

i     a temperature of about 450°C

ii    a pressure of about 2 atmospheres

iii   a vanadium (V) oxide catalyst

Key reactions and equations:

·        Sulfur is burned in air to form sulfur dioxide:

S(s) + O2(g) ® SO2(g)

(Alternatively sulfur dioxide is obtained by heating metal sulfide ores in air. The metal sulfides are converted to the oxides in the process.)

·        Sulfur dioxide is then reacted with oxygen with the conditions stated above in a reversible reaction to make sulfur trioxide:

2SO2(g) + O2(g) ⇌ 2SO3(g)

·        SO3  is reacted with water to make sulfuric acid:

SO3(g) + H2O(l) → H2SO4(aq)

In practice, this reaction is extremely violent.  The sulfur trioxide is absorbed into concentrated sulfuric acid to make an oily liquid called “oleum” (formula H2S2O7) which is then diluted more safely with water.