Application of exact occupation statistics to surface coverage effect on heat of adsorption

Using an exact expression for the number of nearest-neighbor pairs, the exact relations for the change in heat of adsorption of single particles with surface coverage have been calculated within the framework of random distribution taking into account the first, second and third nearestneighbor interactions. It is shown that (1) when the total number of sites is less than about 30, the influence of the corners and edges of a lattice on the heat of adsorption cannot be neglected, and that (2) when the third nearest-neighbor interactions are taken into account for a rectangular or a hexagonal lattice, the heat of adsorption varies with coverage obeying a quadratic equation.