The van der Waals equation of state for water is used to generate isotherms on a pressure-log volume (\(P-V\)) diagram and isobars on a temperature-log volume (\(T-V\)) diagram. Use sliders to change the isotherm temperature on the \(P-V\) diagram and the isobar pressure on the \(T-V\) diagram. Liquid and vapor are in equilibrium within the phase envelope, which is generated from data for water.

The isotherms and isobars have three solutions in the two-phase region, but the only physically-meaningful conditions are the orange dots, which correspond to saturated liquid and saturated vapor. The saturated liquid volume \(V^L\) and the saturated vapor volume \(V^V\) are displayed. The horizontal, dashed orange line (\(P^{sat}\) and \(T^{sat}\)) represents a mixture of liquid and gas. On the \(P-V\) diagram, the green area above the orange line is equal to the area below the orange line when plotted on a linear volume scale.

1. Single-Component P-V and T-V Diagrams. www.youtube.com/watch?v=uhu41n1j9So&t=2s.

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