5 - Open Systems

Abstract

Open systems exchange particles with their environment in addition to work and heat. This exchange entails energy transfer. Internal energy becomes a function of entropy, volume, and moles of particles; its partial derivative with particle mole number is called chemical potential. This is extended to multicomponent systems. The chemical potential of an ideal gas depends on temperature and the logarithm of pressure, with fugacity replacing pressure for real gases. Maxwell relations result by equating mixed partial derivatives and relate measurable physical quantities. Euler’s theorem of homogeneous functions formalizes relationships of extensive and intensive variables, allows integration of fundamental differentials (Euler equation), and connects differentials of intensive variables (Gibbs-Duhem equation). Mole fractions define composition of multicomponent systems. Legendre transformations are developed and used to define new potentials such as Helmholtz and Gibbs free energies. Partial molar quantities are calculated by the method of intercepts. Entropy of a chemical reaction is introduced.