Volume 27, Issue 2

The power of the atomistically founded GENERIC approach to nonequilibrium systems is illustrated by coarse graining from the full N -particle phase space to the level of single-particle distribution functions. For a dilute gas, the elements of GENERIC can be evaluated without any fundamental assumptions. Boltzmann's famous kinetic equation is recovered.

The equations of hydrodynamics are solved for a slow squeeze-Oow in the presence of a gradient of the viscosity which, in turn, is caused by a temperature gradient. The gradient induces an asymmetry of the spreading velocity and a drift of the center of mass towards the direction where the viscosity is decreasing. Due to this phenomenon, adjacent asperites in the friction zone between two solids sliding over each other experience an effective attraction.

The thermodynamic behavior of a black hole, which radiates photons and absorbs energy and matter particles from the surroundings, is given in terms of classical non-equilibrium thermodynamics expressed in the four-dimensional curvilinear coordinates. The local rate of the entropy density change is equal to the divergence of the entropy Oow plus a source term. The divergence represents the entropy exchanged between the black hole and the surroundings and accounts for the emission/absorption of photons and the change in composition caused by the matter particles inOow. The entropy source originates from the irreversible processes occurring at the horizon where the infall of energy and matter particles is driven by the gravitational attraction. Considering the given laws of black hole physics, the rate of the entropy change multiplied by T / c 2 gives the rate of mass change. In the frame-work of classical non-equilibrium thermodynamics, the black hole then appears as a system producing entropy during its life, and transforming into entropy, and then into mass, the work done by the gravitational attraction.

Since Langmuir published the derivation of his famous adsorption isotherm equation in 1918, hundreds of papers on the kinetics of gas adsorption on solid surfaces have appeared in the world literature. Until the early fifties of the 20th century, these were mainly papers reporting on experimental studies of the kinetics of adsorption in various adsorption systems. Surprisingly, although the Langmuir isotherm described the adsorption equilibria fairly well, the related kinetic expressions generally failed to describe the adsorption kinetics. So, beginning in the early fifties, vigorous attempts were made to improve that kinetic approach based on ideas of the Absolute Rate Theory (ART). Since then, one has been able to see more progress on the theoretical side than in the related experimental studies. However, the vast majority of these papers treated hypothetical adsorption kinetics in virtual adsorption systems with well-defined surfaces. This was especially true in the case of the theoretical studies of isothermal adsorption kinetics. Certain progress was made in theoretical studies of the kinetics of thermodesorption, where the energetic heterogeneity of the real solid surfaces was demonstrated in an impressive way. Here, almost all the attempts to take energetic surface heterogeneity into account were based on a further generalization of the ART approach. In the early eighties a new family of fundamental approaches appeared, linking the rate of adsorption/desorption processes to the chemical potentials of the bulk and the adsorbed molecules. Among them the so-called Statistical Rate Theory (SRT) has received the most advanced theoretical attention. The new SRT approach has been generalized during recent years for the case of energetically heterogeneous surfaces. This has been done for both the isothermal kinetics and the kinetics of thermodesorption. So we have only two fundamental approaches which have been generalized for consideration of the kinetics of gas adsorption in the real systems, i.e. the ART and the SRT approaches. The purpose of the present review is to discuss the features of the adsorption kinetics in real adsorption systems, where the solid surface energetic heterogeneity is the main factor determining these features. For that purpose we will thoroughly analyze existing and possible future generalizations of both the ART and SRT approaches, taking this crucial physical factor into account. Next, we will apply the obtained theoretical expressions to quantitatively simulate the observed adsorption kinetics in real adsorption systems. Our study does not refer to the special case of the kinetics of sorption by porous media where the exchange of mass between the gas and the adsorbed phase may not be assumed as the only possible rate-controlling step.