Explain solid salt and saturated aqueous solution?

In this example, the equilibrium system consists of crystalline PbCl₂ and an aqueous phase containing the species H₂O, Pb²⁺ (aq), and Cl^-(aq).

Applying the components approach to this system is straightforward. The solid phase is prepared from PbCl₂ and the aqueous phase could be prepared by dissolving solid PbCl₂ in H₂O. Thus, there are two components and two phases:

F = 2 + C - P = 2

For the species approach, we note that there are four species (PbCl₂, Pb²⁺, Cl^-, and H₂O) and two independent relations among intensive variables: