Question

Calculate configurational entropy (T=0) of N hydrogen atoms on a surface of Pt, which is represented by M possible sites for H atoms. Suppose we have CO molecules, what will change?

Answer 1

There are two types of chemisorbed hydrogen on platinum. The one type decreases the work function and the resistance, and predominates at high temperatures. The other type of adsorption increases the work function and the resistance, and its effect is only detectable at very low temperatures and at low coverage.

--------------- H
Pt-H or Pt / \ Pt, but two different bond strengths depending on different
crystal faces, adatoms more weekly bonded must be readily removed and associated as well with the appropriate band position at lower wave length.

The configurational entropy is related to the number of possible configurations by Boltzmann's entropy formula. A simple way to introduce the Boltzmann entropy is to use the concept of combinatorial
disorder.

S = kb * ln (W) where kB is the Boltzmann constant and W is the number of possible configurations.

For thermodynamic systems where microstates of the system may not have equal probabilities, the appropriate generalization, called the Gibbs entropy, is:

S = -kb * Σ pi ln (pi)

This reduces to equation (1) if the probabilities pi are all equal. Boltzmann used a [pi ln pi] as a density in phase space—without mentioning probability—but since this satisfies the axiomatic definition of a probability measure we can retrospectively interpret it as a probability anyway.

If you add CO there will be more disorder of atoms more probabilities of a higher energy. I hope this can help you understand the fundations of statistical thermodynamics.