I am having some trouble fully understanding the basics and I just wanted to see if somebody would please clarify this for me. First, say you have a one component system in two phases: vapor and liquid. Gibbs' phase rule restricts the system to one independent, intensive variable that may be specified. Am I correct in saying that the mole or mass fraction of the system in the vapor phase does not count as an intensive variable? What about an "overall" property, like the two-phase density? These wouldn't count as intensive variables, right? Then is it impossible to find them through calculation even if the system is specified? Second, say you have a two component system in two phases: vapor and liquid. Gibbs' phase rule restricts the system to two independent, intensive variables that may be specified. But this time, variables like chemical composition of each phase (e.g. vapor mole fraction of component 1, y1, liquid mole fraction of component 2, x2) DO count as intensive variables, right? What about overall chemical compositions (e.g. total mole fraction of component 1, z1) or total vapor fraction (yT). Are these intensive or extensive variables? Can overall mole fractions or total vapor fraction be found if the chemical compositions of each phase are known? I know this is probably a simple question and it's kind of embarrassing to ask, but I couldn't find anything that clearly explained this for me. I find it odd (if I'm right) that vapor fraction counts as an extensive variable for a one component, two-phase system, but it counts as an intensive variable when another component is introduced. I just want to make sure this is right. Thanks.