(i) Contact process consists of three steps. First is the burning of sulphide ores to form SO₂ gas. 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.

(ii) The forward reaction is exothermic and there is a decrease in a number of moles and volume. 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.