Enthalpy–entropy compensation for isosteric state adsorption at near ambient temperatures

Abstract

The adsorption process at near ambient temperatures indicated that the EEC (enthalpy–entropy compensation) is affected by three basic thermodynamic values: ∆H, ∆S and T. The consequence is that it is possible to determine an isosteric straight (symbol H − S) without experimental studies based on the slope coefficient Tiso, which is the constant arising from the expected temperature range (about 0–60 °C). Therefore, EEC curves can be obtained by appropriate modification of the temperature range. In the case of entropy of adsorption, the decisive influence is the entropy of gas. For visualization and characterization of this impact, we proposed resolute pointer µ (Eq. 25), through which it is observed that for small values of the equilibrium vapor pressure, as P → 0, there are significant deviations from the isosteric straight H − S. The case where P → P0 followed a gradual grouping of experimental data in accordance with the relationship with H − S. We used the three-parameter equation for exothermic processes. For the extrapolated conditions, the so-called point of zero adsorption represented the enthalpy and entropy of adsorption, whose values are analogous to previous results in the literature, which can be considered an appropriate analytical method to determine these two thermodynamic values.