The necessary conditions for getting maximum yield of ammonia are as follows :

(i) Low Temperature : As the reaction is exothermic in nature, so the temperature should be low. When temperature is lowered, the rate of the reaction slows down and the yield is maximum. It is found for maximum yield, temperature should be between 450° to 500°C (optimum temperature).

(ii) Catalyst : A catalyst is used to accelerate the reaction at optimum temperature.

Following are the catalysts used:

(a) Finely divided iron, mixed with molybdenum as promoter.

(b) A better catalyst is ferric oxide (Fe₂O₃ ) containing 1% of potassium oxide (K₂O) and 3% of aluminium oxide (Al₂O₃ ) which acts as promoters.

(iii) High Pressure : When 4 volumes of a mixture of nitrogen and hydrogen are reduced to 2 volumes of ammonia, the pressure drops. In order to have maximum yield the pressure should be very high. The optimum pressure should be between 200 atmospheres to 900 atmospheres.

(iv) Purity of Gases : Any kind of impurity tends to slow down the reaction or poisons catalyst. So, the gases that are to be used should be pure and dry.