The pressure-volume phase diagram (pressure versus log of molar volume) is shown for water. This demonstrates typical phase behavior of a single component and illustrates the concept of state functions. Drag the black dot on the P-V plot to change pressure and volume (and temperature also changes). The piston-cylinder represents the log of the volume, so that the large differences in volume between vapor and liquid can be visualized. The fluid in the cylinder is blue when liquid, and the intensity of the color increases as the fluid becomes denser. As the fluid becomes more gas-like, the color changes to green, and the green color becomes less intense as density decreases