Final answer:
The formation of [Cu(NH3)4]2+ at 25°C involving the exchange of water molecules for NH3 ligands around a copper ion is typically spontaneous, as indicated by the Formation Constant and suggested by the observable color change, implying a stable complex formation.
Step-by-step explanation:
The student asks if the formation of [Cu(NH3)4]2+ at 25°C is spontaneous or nonspontaneous with a negative ΔG°. Given the context of complex ion formation, especially that of copper ammonia complexes, this process is associated with the Formation Constant. The complexation reactions typically involve the substitution of water molecules by stronger ligands such as NH3. In the case of the formation of complex ions involving copper ions and ammonia, the intense color change observed (from pale blue to blue-violet) implies a strong interaction between Cu2+ and NH3, forming a more stable complex and driving the equilibrium to the right.
This is a classical equilibrium process where ligands replace water molecules, and such reactions are usually spontaneous if the ligand provides greater stability to the metal ion. Although no direct data are provided for the Gibbs free energy change pertaining to this process, based on the described process, it is suggestive of spontaneity at room temperature.