Sulphuric Acid Manufacture

The key step of the Contact process is 2SO_2 + O_2 ⇌ 2SO_3, an exothermic, mole-reducing reaction. Because it is exothermic, a low temperature thermodynamically favours a higher yield of sulphur trioxide, but at low temperature the rate is too slow for industrial production. Therefore a moderate optimum temperature around 720 K is used together with a vanadium pentoxide catalyst, which speeds the attainment of equilibrium without shifting its position, giving a good yield at a practical rate. The option that the conditions make the reaction endothermic is wrong, since the reaction is intrinsically exothermic. The option to decrease pressure is incorrect, as moderate to high pressure favours the fewer-mole product side. The option to avoid using any catalyst contradicts the use of V_2O_5. This balancing of yield and rate is a standard NCERT industrial concept. Carefully relating the data to the governing principle ensures the reasoning remains valid even when the numbers or species in the question are changed. Understanding sulphuric acid manufacture in this way ties directly into the wider study of p-block elements, where the same reasoning recurs across many problems. Plausibility check: choosing a moderate temperature with a catalyst reconciles Le Chatelier's preference for low temperature with the kinetic need for speed, confirming the reasoning.