-the higeher the temperature,the small is the percentage of ammonia at equilibrium.
Therefroe to goet the maxium amount of ammonia we need a very high pressure and a very low temperature.in practice,a high pressure of about 200 atmosphereis used.Usingg higher pressures would produce even more ammonia,but this involes extra expense,and there is a safety risk.
It is not realistic to use a very low temperature of about 100 C, beacause the raction would be far too slow and irt would take a very long time to reach rquilibrium. Therefore ,a modertaly high tempresture of 450 C tis used as a comporomis ,even though the amount of ammonia at equilibrium is reduced.