According to Le Chatelier's Principle: What happens when you add DIFFERENT species to the equilibrium?

1 Answer
Sep 28, 2015

Le Chatelier's principle applies to equilibrium concentrations in specific equilibria. Addition of different species that affect these equilibrium concentrations, will change the equilibria accordingly.

Explanation:

Consider the solution behaviour of a sparingly soluble or insoluble salt at equilibrium, say AgCl.

We write AgCl(s)Ag++Cl(i)

To describe this reaction, we write Ksp=[Ag+][Cl]. Should we add aqueous ammonia we will reduce the [Ag+] value because of the following competing equiibrium:

Ag++2NH3[Ag(NH3)2]+(ii)

More silver ion, [Ag+], will enter solution because it can be complexed by the ammonia. To give an answer in terms of Le Chatelier's principle, because we reduce [Ag+] in equilibrium (i), we can drive the equilibrium to the right hand side.

On the other hand, for equilibrium (ii), if we reduce [NH3], say by increasing the pH to form NH+4, we would drive the equilibrium to the left. Of course, we are dealing with competing equilibria, that may be difficult to calculate.