Mixtures

So far, we have studied simple substances, i.e., materials that do not change their composition. In this chapter we begin the discussion of mixtures of varying composition—either through mixing, or chemical reactions—by introducing the relevant thermodynamic properties required for their description. The composition is given through either mole or mass fractions, which appear as additional variables in the thermodynamic properties (pressure, energy, enthalpy, entropy... ) of the mixture. For ideal mixtures, these properties can be deduced from the properties of the separated components. In non-ideal mixtures, however, mixing effects come into play that lead to mixing volume and enthalpy of mixing. In either case the entropy of mixing plays an important role for the mixing behavior, and is directly related to the work required for separation.