Chapter 3 - Entropy as a state property

Abstract

The second law of thermodynamics provides a physical state property called entropy as an extensive variable relating to the capacity of energy distribution over the constituent particles in a physicochemical system. This chapter discusses the creation of entropy due to the advancement of an irreversible process in a system, and elucidates the change in entropy caused by heat transfer, gas expansion, and mixing of substances. The energy of a physicochemical system is dependent on the substances that make the system. The substances, though macroscopically forming phases, are microscopically comprised of particles, such as atoms, ions, and molecules constituting a particle ensemble. The energy of the system is distributed among individual particles in the ensemble, and the energy distribution over the constituent particles plays an important role in determining the property of the physicochemical system. The second law of thermodynamics defines a state property called entropy as an extensive variable relating to the capacity of energy distribution over the constituent particles. The energy of a system is not uniformly shared among the individual constituent particles but unevenly generating high and low energy particles.