Onsager relationships

This chapter discusses Onsager relationships. These relationships result from the linear response at the macroscale off-equilibrium from the reversibility of the microscale and represent an example of cause and chance at work. Flux-flow formalism—flux densities tied to thermodynamic forces—is developed to build the generalized linear relationships for heat, electric, chemical composition and free energy. The relationships are then applied to examples from previous chapters—thermoelectric and others—to show how results of interest can be derived more easily through exploiting Onsager relationships’ linearity and reciprocity relationships. The chapter discusses Onsager relationships with respect to Ohm’s law, Fourier’s law, Fick’s law, Darcy’s law, Gibbs free energy, thermoelectric effects and fluctuation-dissipation.