Now figure out how to get the same no of
atoms of each kind on both sides by using
whole no coefficients in front of the species.
As       H2  + _N2 NH3, then
           H2  + _N2 _ NH3,  then
          _ H2  +  _N2 _ NH3
Now have _ H’s, _N’s on both sides and the
lowest set of whole no coefficients have
been used.  The equation is balanced.