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

1 Answer
Sep 28, 2015

Answer:

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) rightleftharpoons Ag^+ + Cl^- ##(i)#

To describe this reaction, we write #K_(sp) = [Ag^+][Cl^-]#. Should we add aqueous ammonia we will reduce the #[Ag^+]# value because of the following competing equiibrium:

#Ag^+ + 2NH_3 rightleftharpoons [Ag(NH_3)_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 #[NH_3]#, 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.