Question

So NH3 +HCl= NH4+ + Cl- can we actually say that NH4+ + Cl-= NH3 +HCl??

Answer 1

Sometimes chemical reactions are reversible, and can be written in reverse. Other times they can not. For example, in a combustion reaction, once the products are formed they can not be converted back to the original reactants.

If a chemical reaction can occur in both directions, it will be spontaneous in one direction, but non-spontaneous in the other direction. In a closed system, the reaction could also reach chemical equilibrium, where the forward and reverse reactions still occur at equal rates, such that no macroscopic changes are visible.