Retain separate liquid and vapor composition coordinates when reading a vapor-liquid equilibrium result.
Define the Phase or Process Boundary
LearnChemE's flash equations uses x for component mole fraction in liquid and y for the fraction in equilibrium vapor. Overall feed composition z describes the combined inventory. These quantities can differ even when both phases are at the same temperature and pressure.
Review a Hypothetical Comparison
In an invented binary sample pair, liquid contains x_A=0.20 and vapor contains y_A=0.60. Their other-component fractions are 0.80 and 0.40. An overall composition z_A=0.35 is a third coordinate, not a replacement for either measurement. Plotting (0.35,0.60) as the measured equilibrium pair would join a bulk-inventory value to a phase-specific value and misstate the observation.
Keep the Evidence with the Decision
Use a phase-labelled sample record: component identity, mole or mass basis, temperature, pressure and sampling state. Mark the liquid and vapor coordinates as a matched pair. Preserve the bulk composition in a separate field for a later material balance. The same numeric label on an unlabelled sample bottle does not identify its phase.
The assigned fractions illustrate coordinate handling. They establish no real mixture equilibrium, volatility model or separator capability. Mass fractions require a consistent conversion before they are used in equations written for mole fractions.
Which measured phase composition belongs in the equilibrium comparison?
This blank worksheet is for your own project. It contains no H M machine trial result.
| Review field | Reference or result | Responsible person |
|---|---|---|
| Component and mole-fraction basis | To complete | To complete |
| Matched liquid sample x | To complete | To complete |
| Matched vapor sample y | To complete | To complete |
| Overall inventory z and equilibrium state | To complete | To complete |
Customer Questions
Can x and y be equal?
Yes at some states; equality must come from the actual equilibrium evidence.
Is z another name for x?
No. z represents the overall inventory, while x identifies liquid composition.
Can one pair predict all compositions?
No. Retain the applicable temperature, pressure and mixture model.
Primary References
These references support the technical principles discussed in this guide. The worked examples and review questions are educational.
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