This P-x-y diagram shows the regions of phase stability for a benzene-toluene mixture at 20°C. This mixture is modeled as an ideal solution that obeys Raoult’s law. The solid red line is the bubble pressure and represents the liquid mole fraction. The solid blue curve is the dew pressure and represents the vapor composition. Click and drag the purple dot to adjust the mixture’s pressure and mole fraction of the benzene. When two phases co-exist, a horizontal line (the dashed line in the diagram, a tie line) through the purple point intersects the bubble and dew pressure curves at the liquid and vapor compositions, respectively, that are in equilibrium. The relative amounts of liquid and vapor, which are shown in the bar graph, are calculated using the lever rule.