Entropy behavior for isolated systems containing bounded and unbounded states: latent heat at the inflection point

Abstract

Systems like the Morse oscillator with potential energies that have a minimum and states that are both bounded and extended are considered in this study in the microcanonical statistical ensemble. In the binding region, the entropy becomes a growing function of the internal energy and has a well-defined inflection point corresponding to a temperature maximum. Consequently, the specific heat supports negative and positive values around this region. Moreover, focusing on this inflection point allows to define the critical energy and temperature, both evaluated analytically and numerically. Specifically, the existence of this point is the signature of a phase transition, and latent heat dynamics occur to accomplish the transition. The conditions established below apply to a large variety of potentials, including molecular ones, and have relevance for physics, chemistry, and engineering sciences. As a specific application, we show that the inflection point for the H2 molecule occurs at −1.26 [eV].