Chapter 12 - Equilibrium

Abstract

A system is said to be in an equilibrium state when it is closed for mass exchange, provided that the transition frequencies are time-independent. The state is most easily described in the framework of the kinetic approach to nucleation. The equilibrium cluster size distribution C(n) is easily obtained from the condition expressing the principle of detailed balance or microscopic reversibility, which forbids the flow of local fluxes along the size axis. Finding the equilibrium cluster size distribution C(n) in this way is particularly important theoretically because this quantity is also obtainable by thermodynamic considerations. A comparison of the kinetic and thermodynamic results for C(n) makes it possible to establish the connection between nucleation kinetics and thermodynamics. At equilibrium, the concentration of the clusters of various sizes does not change with time. The chapter also examines C(n) kinetically. For an undersaturated or saturated old phase and when the system is in truly stable equilibrium, C(n) represents the really existing population of clusters in the system. However, when the old phase is supersaturated and thus in metastable equilibrium, C(n) is only an imaginary cluster size distribution describing the cluster population that would set up in the system if truly stable equilibrium were possible.