P Block Elements

7.24

Contact process consists of three steps. First is the burning of sulphide ores to form SO2 The second step (key step) is SO₂ is oxidised to SO₃ by heating the mixture on the heterogeneous catalyst V₂O₅.

Now, this step is very crucial for maximising the yield of H₂SO₄ It can be done by controlling the temperature and pressure of reaction.

The forward reaction is exothermic and there is a decrease in a number of moles and As Le- Chatelier principle states that when a system experiences a disturbance (concentration, pressure changes) it will respond to nullify the changes produced to bring initial condition.

So, when we decrease temperature (BEING EXOTHERMIC),

it will try to restore original equilibrium, by experiencing a forward reaction where the temperature is high.

Now in case of pressure, moles of product is less than that of reactant and we know that no. of moles is directly proportional to volume (pressure is inversely proportional to volume). So volume of reactant is more than product if we increase pressure (decrease volume) the reaction will shift to forward direction.

NOTE: The optimum conditions to maximise the yield of sulphuric acid is the pressure of 2-3 atm and temperature around 723K.

7.23

 H₂SO₄ is one the most important and widely used chemicals for many purposes. It has following uses:

As an electrolyte sulphuric acid dissociates in aqueous solution to form ions. These ions are responsible for the conduction of electricity. As a result, sulphuric acid is used in the manufacture of the lead storage battery.

As a dehydrating agent (to remove water) because it has a great affinity for water. It doesn't get dissolved in water but absorb it, so it is used as a drying

For removing layers of basic oxides from the metal surfaces like iron, copper, before the metals are galvanized, electroplated. Because when the metals are dissolved in sulphuric acid the basic oxide layer formed (due to reaction with air, water) will be dissolved in it as it is acidic in nature.