Thermodynamics, Statistical Physics, and Quantum Mechanics

THERMODYNAMICS AND STATISTICAL PHYSICS 233

where the possible occupational numbers of the site for a submonolayer

0,1 (site is empty, site isoccupied),withenergy Performing

the sums, we have

The averagenumber ofparticles persite may bewritten

The total number ofadsorbedparticlesNis given by

The surfaceconcentration issimply

(S.4.102.9) canalso bederived by consideringthe canonicalensemble. The
number ofpossible ways ofdistributingNatomsamong sites is

where

and

Substituting for anideal gasfrom(S.4.102.4)into(S.4.102.9), we have