The thermodynamic state functions and partition functions for adsorbates on solid surfaces are often treated with the 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. Expressions for equilibrium constants and rate constants within transition state theory (TST) differ between these three models. Expressions will be presented for the equilibrium constants and rate constants of common surface reaction types in terms of the standard-state free energies (and enthalpies plus entropies) of adsorbates and adsorbed transition states, and their molar partition functions. When these are used, one must choose standard-state concentrations, since both entropy and the molar partition function depend upon concentration. Some common pitfalls which occur when doing this that lead to large errors will be discussed.

Equilibrium constants and rate constants for adsorbates in microkinetic modelling: 2D gas, 2D lattice gas, and hindered translator models

255th National Meeting (2018)

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