DIFFUSION AND THERMOKINETICS

Abstract

Diffusion is a process of transport controlled by the random movement of mobile particles in fluid systems. The rate law of diffusion had been formulated by more different manners. The linear `Fick-type´ laws (the diffusion flux is proportional to the gradient of the concentration or activity) are based on experimental observations. The likewise linear force law (the diffusion flux is proportional to the chemical potential gradient) is one of the `Ohm-type´ laws of the irreversible thermodynamics. Both are in conflict with each other and with some general principles (equilibrium criteria, relativity theory). Applying the thermodynamic kinetic theory (called `thermokinetics´) it turns out that both linear laws are approximations of an exact but nonlinear equation the GeneralForce Law (GFL).