Question

Apply the Physico – Chemical principle in the manufacture of Sulphuric acid by contact process. 

Answer 1

Physico-Chemical principles in sulfuric acid production

Temperature

Sulfur dioxide and oxygen then react as follows:

According to the Le Chatelier's principle, a lower temperature should be used to shift the chemical equilibrium towards the right, hence increasing the percentage yield. In order to get as much sulphur trioxide as possible in the equilibrium mixture, you need as low a temperature as possible.

Pressure

Notice that there are 3 molecules on the left-hand side of the equation, but only 2 on the right. According to Le Chatelier's Principle, if you increase the pressure the system will respond by favouring the reaction which produces fewer molecules. That will cause the pressure to fall again. In order to get as much sulphur trioxide as possible in the equilibrium mixture, you need as high a pressure as possible. High pressures also increase the rate of the reaction.

Concentration

• An excess of oxygen relative to the proportions demanded by the equation.

 

According to Le Chatelier's Principle, Increasing the concentration of oxygen in the mixture causes the position of equilibrium to shift towards the right. Since the oxygen comes from the air, this is a very cheap way of increasing the conversion of sulphur dioxide into sulphur trioxide.By increasing the proportion of oxygen you can increase the percentage of the sulphur dioxide converted, but at the same time decrease the total amount of sulphur trioxide made each day. The 1 : 1 mixture turns out to give you the best possible overall yield of sulphur trioxide.