Phase Behavior on a Pressure-Volume Diagram
Phase Behavior on a Pressure-Volume Diagram
A log pressure versus log volume phase diagram is shown for water; this shows typical phase behavior of single-component systems and illustrates the concept of state functions. Use sliders to move the black dot around at constant pressure or constant volume, or check the "drag point" box to click and drag the dot around the - diagram. The piston-cylinder represents the volumes of liquid and vapor present. Select the log or linear volume representation to view the piston-cylinder on a log or linear scale. When two phases are present, a pop-out shows a magnified view of the liquid and vapor volumes on the linear scale. Liquid in the cylinder is blue and vapor is green, and the intensities of these colors increase as their densities increase.
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Note that the liquid, vapor, supercritical, and two-phase regions are labeled, but no boundaries exist between the single-phase regions (liquid, vapor, supercritical). This diagram can be used to illustrate circumnavigating the critical point, which is the highest temperature and pressure where two phases coexist (647 K, 22.1 MPa for water). To do so, check "drag point" and drag the black dot from the liquid phase region to the supercritical region and then to the vapor phase region without a phase change (i.e., without two phases coexisting). By contrast, at a constant pressure below the critical pressure, if you drag the dot from a small volume to large volume, two phases are observed.