How many variables can be fixed independently in order to fix the state of a binary mixture in vapor–liquid equilibrium if, as is most often the case, the two phases contain both components in different amounts? Which variables would you decide to control in an actual experiment? How many degrees of freedom characterize a mixture in vapor–liquid equilibrium in the case where the mixture forms an azeotrope, that is a mixture in vapor–liquid equilibrium featuring vapor and liquid with the same composition?