DIFFUSION AND THERMOKINETICS

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