Standard States for Adsorption on Solid Surfaces: 2D Gases, Surface Liquids, and Langmuir Adsorbates

Abstract

Standard states are utilized to compare thermodynamic data obtained from different experiments and calculations, and this ability to compare thermodynamic data plays an important role in science and society. For molecules adsorbed on surfaces, there are currently no universally accepted standard states. Here, standard states are proposed for the different types of molecular adsorbate phases, with the intent to enable physical insight to be gained by tabulating experimental/calculated values, such that comparison between different systems and existing societal tabulations of chemical standard state tabulated values can be done directly. A “density based” standard state is proposed for 2D gases, and a “relative coverage based” standard state is proposed for immobile adsorbates and nonislanding 2D liquids. These units are chosen based upon the units which the activity depends on. The standard states recommended here are chosen due to the entropies associated with them, such that physical insight can be gaine...