Heat a mixture and the vapour that leaves is not the liquid you started with. The still, the molecules and the phase diagram here all answer that one question at once.
VLE from Antoine vapour pressures with van Laar activity coefficients · 1 atm
The still 00:00
150 W
none
In the pot
—
Boiling-point diagram
click the plot to recharge
Readout
Pot
—
Thermometer at the head
—
Liquid in the pot x—
Vapour above it y—
Arriving at the condenser—
Collected in the receiver—
At molecular scale
How this panel is drawn, and what it leaves out
What you are looking at
Why a column beats repeated distillation
The run so far composition and head temperature against how much has come over
distillate coming over nowreceiver, running averageliquid left in the pothead temperature (right axis)