For , continuous removal of NH3 maintains the following condition

Due the removal of Nh3, numerator decreasesi.e. QC α [NH3]2 due to decrease in the concentration of NH3, QC decrease. QC < KC (KC is always a constant at given temperature)In Such cases QC must increase to be come equal to KC which can happen only when more amounts of N2 and H2 react with each other.Thus forward reaction is favoured.