N2(g)+3H2(g)⇌2NH3(g);∆H=−93.6kJ In above reaction, number of molecules are reducing from left to right. According to Le-Ch atelier when we create any boundation. Then reaction will shift in a direction to neutralize the effect of boundation. When we reduce the pressure in above reaction then reaction will shift into backward direction where number of molecules are increasing. Hence, the yield of ammonia does not increase when pressure is decreased.