(i) Favourable conditions for the manufacture of ammonia by Haeber Process:
(i)    A high temperature of 400-500°C.
(ii)    A high pressure of 200-1000 atoms.
(iii)   A catalyst usually Fe + Mo or finely divided iron and Fe₃O₄ containing small amounts of K₂O and Al₂O₃.

(ii) Favourable conditions for the manufacture of sulphuric acid by contact process:
(i)    High concentration of oxygen : Air or oxygen used for the oxidation of sulphur dioxide to sulphur trioxide must be in excess. Furthermore, these gases must be absolutely pure otherwise they will poison the catalyst.
(ii)    High pressure: Since the forward reaction proceeds with decrease in volume, therefore, high pressure will favour the reaction. In actual practice, a pressure of about 2 atmospheres is used. This is because gases are acidic and corrosion of the plant occurs at high pressure.
(iii)    Low temperature : Since the forward reaction is exothermic, therefore, low temperature will favour the reaction. However, rate of the reaction decreases with decrease in temperature. Therefore, the reaction is carried out at an optimum temperature of 623-723 K.
(iv)    Use of catalyst: To increase the rate of a reaction at low temperature, a catalyst is to be used. The commonly used catalysts are platinum, or divanadium pentoxide (V₂O_s). Since platinum is quite costly and is easily poisoned by arsenic impurities usually present in SO₂, therefore, these days, divanadium pentoxide is employed because it is not only cheaper but is also not easily poisoned.
(v)    Purity of gases: Purity of gases is another essential conditions for the maximum yield of SO₂. The impurities present in the reacting gases act as catalytic poison and thus decrease the efficiency of the catalyst.