Equilibrium Constants and Rate Constants for Adsorbates: Two-Dimensional (2D) Ideal Gas, 2D Ideal Lattice Gas, and Ideal Hindered Translator Models

Abstract

The thermodynamic state functions and partition functions for adsorbates on solid surfaces are often treated with two-dimensional (2D) ideal gas and 2D ideal lattice gas models. These are idealized limits of the real situation for adsorbates on solid surfaces, which are more accurately described as hindered translators. We describe a simple extension of the ideal 2D gas model to a more realistic ideal hindered translator model based on our recent approximation for the partition function of ideal hindered translators [Sprowl et al., J. Phys. Chem. C., 2016, DOI: 10.1021/acs.jpcc.5b11616]. Expressions for equilibrium constants and rate constants within transition-state theory (TST) are derived in a self-consistent formalism based on both partition functions and standard-state entropies. The mixing of these three adsorbate models (ideal 2D gas, ideal 2D lattice gas, and ideal hindered translator) within the same equilibrium or rate constant calculation is sometimes necessary but requires careful and consiste...