equation Nh4Cl+NaOH=NaCl+H2O+Nh3 is an impossible reaction. why?

Please note that the reaction of ammonium chloride and sodium hydroxide is not an impossible reaction. This reaction is a very common reaction in which NaOH, being the stronger base decomposes NH₄Cl to give NaCl, NH₃ and H₂O. 

                                        NH₄Cl + NaOH → NaCl + H₂O + NH₃