In this Demonstration, liquid propane or liquid toluene is injected into an evacuated 2-L spherical tank that is held at constant temperature. When propane is injected, it either vaporizes completely or forms two phases in vapor-liquid equilibrium (VLE), depending on the number of moles injected and the temperature (control both with sliders). Because toluene has a much lower saturation pressure, only a small amount of injected toluene liquid vaporizes. When the component is in VLE, the tank pressure equals the saturation pressure; otherwise, the pressure is calculated using the ideal gas law. The pressure is displayed at the top of the tank. Click the play button next to "inject liquid" to inject liquid into the tank. The intensity of the blue color of the vapor is proportional to the vapor density. The liquid volume in the tank is exaggerated relative to the vapor volume for better visualization. The bar graph on the right shows the number of moles of liquid and vapor in the tank.