Name the principle which helps better yield of ammonia.

• Since the reaction is exothermic, hence low temperature will favour the synthesis. In practice the optimum temperature has been found to be in the range of 450-500^OC.
• Four volumes of reactants produce two volumes of product; hence high pressure favours the formation of ammonia. The optimum pressure is found to be 200 to 900 atm.
• Finely divided catalyst like Fe can improve the speed of the reaction and a promoter like molybdenum is used to increase the efficiency of the catalyst.
• Since the reaction is exothermic, external heating is not required after the reactants are initially heated.