Hi I am struggling immensely with understand some aspects of chemical thermodynamics: 1) Lets say I have a solid with N atoms and am examining the ionization of individual atoms, and I am supposed to think of the electrons as ideal gasses. Or, 2) a solid or liquid is in thermal equilibrium with its gas form (again the gas is an ideal gas). So, I am examining the vapor pressure. In such exercises, I am sometimes expected to use the grand canonical ensemble and other times the canonical ensemble. However, I do not get: Why do I use the grand canonical ensemble in 1 but not in 2? How can I tell if the chemical potential is significant enough to use the grand canonical ensemble? Why is the chemical potential for electrons bonded to the solid the same as the ideal gas? What is the energy of electrons bonded to atoms versus the ones that are not bonded? What chapter in what book should I read in order to understand this?