# Adding a Second Component to a Fixed-Volume Container

A constant-volume tank initially contains one component in the vapor phase (either -octane or -hexane), and you can add the other component at constant temperature using a slider. Change the temperature with another slider. Select the component to be added with buttons. The pressure-composition diagram has a blue line for the bubble pressure and an orange curve for the dew-point pressure. The black dot is located at the overall composition and the pressure. When two phases are present, the -hexane mole fractions of the liquid phase ( ) and the vapor phase ( ) are displayed. The bar graph represents the number of moles of each component in the liquid and vapor phase; purple is for -hexane and green is for -octane.

### DETAILS

The saturation pressures are calculated using the Antoine equation: ,
where is the saturation pressure (bar) of component ; , and are Antoine constants; and is temperature (K).
Raoult's law for a binary mixture is used to calculate the bubble and dew pressures: , ,
where and are the liquid mole fractions of each component and and are the vapor mole fractions .
The overall mole fraction of component 1 is , where and are the total moles of each component.
When only vapor is present, , ,
where is pressure (bar), is the gas constant ([L bar]/[mol K]), is volume (L) and are moles of vapor.
The following five equations are solved for , , , , and liquid moles when both liquid and vapor are present.
From Raoult's law: , .
From overall and species mole balances: , .
From a volume balance: ,
where is the molar density of the mixture (mol/L).
The screencast video at  explains how to use this Demonstration.
Reference

### PERMANENT CITATION

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