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Acids and Alkalis

Manufacture of Sulfuric Acid  -  The Contact Process.

The Reaction of Oxygen with Sulfur Dioxide to make Sulfur Trioxide.

Sulfur dioxide
is made by reacting sulfur with oxygen.

Sulfur dioxide can be made to react with more oxygen
to make sulfur trioxide.
This is another example of oxidation.

The reaction is reversible (shown by the reversible arrow arrow).
The forward reaction (from left to right) is

This is the balanced chemical equation for the reaction of
sulfur dioxide with oxygen.

sulfur dioxide oxygen  reversible arrow  sulfur trioxide.
2SO2(g)        +    O2(g)    reversible arrow         2SO3(g)

The industrial conditions for the chemical reaction are
1) The Temperature is 450 °C.
2) The Pressure is between 1 and 2 atmospheres.
3) A Vanadium(V) oxide (V2O5) catalyst is used.

About 99% of the sulfur dioxide
is converted into sulfur trioxide under these conditions.
The sulfur trioxide is used to make sulfuric acid.

The effect on the rate of the reaction and
the yield which you get from a reversible reaction
depends on the conditions (temperature, pressure and catalyst).
These have been summarized for the Haber Process.

1. Increasing the temperature favours the endothermic reaction.

2. Increasing the pressure favours the smaller volume.

3. Using a catalyst gives the equilibrium conditions more quickly.

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