28. A graph of three variables (such as P, V, & T) requires three dimensions and is often a surface rather than a line as for the 2-D graphs. A 3-D Phase diagram (with only one component): A surface representing the properties of a typical pure substance (what a theoretical equation of state would have to account for) Each point on the curving surface represents a set of values of the pressure, temperature, and molar volume that can be attained by this substance.
29. Two-component Phase Diagrams (Temp vs. Composition) Gibbs’ Phase rule for a two-component system: F + P = C + 2, where C=2 so, F + P = 2 + 2 = 4 so, F = 4 – P for one phase (P=1) F=3 which is a space, not restricted to the area of any 2-D graph. for two phases (P=2) F=2 which is an area or surface for three phases (P=3) F=1 which is a line for four phases (P=4) F=0 which must be a point, such as an azeotrope or a eutectic point.