Acids and Alkalis

Manufacture of Sulfuric Acid  -  The Contact Process.

The Effect of Temperature on the Formation of Sulfur Trioxide.

The formation of sulfur trioxide is reversible.

The forward reaction (from left to right) is exothermic
(compare this with the formation of ammonia in the Haber process).

sulfur dioxide   +  oxygen    sulphur trioxide
2SO_2(g)        +     O_2(g)            2SO_3(g)

Increasing the temperature will increase the rate of the reaction
but decrease the amount of sulfur trioxide in the equilibrium mixture.

The temperature of 450 °C is a compromise between
the amount of sulfur trioxide in the equilibrium mixture
and the rate at which sulfur trioxide is formed.

The temperature of 450 °C gives the best yield of sulfur trioxide.