In this case we simply have Φ Φ G = − − ⟨ ⟨ P ⟩ ⟩ V , as well as the familiar relationship G = ⟨ ⟨ N ⟩ ⟩ μ μ for the Gibbs free energy. The value of Φ Φ G can be understood as the work that can be extracted from the system by shrinking it down to nothing (putting all the particles and energy back into the reservoir). The fact that Φ Φ G = − − ⟨ ⟨ P ⟩ ⟩ V is negative implies that the extraction of particles from the system to the reservoir requires energy input.