Figure

Temperature vs. pressure for pure component

These results are conveniently presented in graphic form using several types of "phase diagrams."

A. T-xy Diagrams

If the data are taken with pressure held constant (isobaric), it is convenient to plot two curves on the same paper: temperature versus x and temperature versus y. Figure 2.7 illustrates a typical T-xy diagram. To determine the composition of liquid and vapor phases in equilibrium with each other at a given temperature, and at the pressure under which the data were obtained, one merely draws a horizontal line at the given temperature and reads off x and y values.

B. P-xy Diagrams

Data taken at constant temperature (isothermal) are plotted as two curves: pressure versus x and pressure versus y, as illustrated in Figure 2.8. Note that the ends of the curves must intersect at x = y = 0 and at x = y = 1, since these points correspond to pure components, either light or heavy.

(HIGH BOILING POINT!

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