Question

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

Answer 1

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.