1. The problem statement, all variables and given/known data Suppose we put N atoms of argon into a container of volume V at temperature T. Of these N atoms, Nad stick to the surface, while the remainder Ngas = N - Nad form an ideal gas inside the container. Assume that the atoms on the surface are not able to move and have an energy -eo. Furthermore, let Ns >>1 be the number of sites on the surface the atoms can stick to. a)Calculate the entropy of the Nad atoms on the surface. The subscript 'ad' presumably because the atoms are adsorbed onto the surface 2. Relevant equations # of microstates found by combinatorics and entropy given by Boltzmann's Law. 3. The attempt at a solution It seems to me that although we have some stated assumptions more is needed to give an answer that matches the one in the answer key. Is more than one atom allowed to occupy a site on the surface? Are the atoms indistinguishable? From N atoms, Nad are placed on the surface. This can be done in N choose Nad ways. Assuming the atoms are distinguishable, then we multiply this number by Ns!, since there exists that many arrangements of those Nad atoms. If they are indistinguishable, then we do not multiply by Ns!. This is also assuming only one atom can occupy each site. Many thanks.