Final answer:
At equilibrium, the Gibbs free energy change (ΔG) for the dissolution of FeS in water at 25°C is zero because the system is in a state of dynamic equilibrium.
Step-by-step explanation:
The question is related to the solubility product constant (Ksp) and the relationship to Gibbs free energy change (ΔG) at equilibrium. When a compound such as FeS is at equilibrium in a saturated solution, the ΔG for the dissolution process is zero because the system is at equilibrium and no net change occurs over time.
The Ksp value for FeS is given as 6 x 10-18 M, and since this is a non-zero value, it indicates that the dissolution process is thermodynamically favorable. However, since we're interested in the dissolution at equilibrium, the value of ΔG at equilibrium is zero. This is because at dynamic equilibrium, the forward dissolution and reverse precipitation occur at the same rate, with no net energy change in the system.