Solution solute in a solution is the mass of that solute expressed as a percentage of the mass of the whole solution. "Homogeneous" means that the components of the mixture form a single phase. "Heterogeneous" means that the components of the mixture are of different phase. The properties of the mixture (such as concentration, temperature, and density) can be uniformly distributed through the volume but only in absence of diffusion phenomena or after their completion. Usually, the substance present in the greatest amount is considered the solvent. Solvents can be gases, liquids or solids. One or more components present in the
A priori probability case of the hydrogen atom or Coulomb potential (where the evaluation of the phase space volume for constant energy is more complicated) one knows that the quantum mechanical degeneracy is formula_56 with formula_57. Thus in this case formula_58. In statistical mechanics (see any book) one derives the so-called distribution functions formula_59 for various statistics. In the case of Fermi-Dirac statistics and Bose-Einstein statistics these functions are respectively These functions are derived for (1) a system in dynamic equilibrium (i.e. under steady, uniform conditions) with (2) total (and huge) number of particles formula_61 (this condition determines the constant formula_62), and (3)