• Composition a heated to boiling (a2
& > a2)
• Vapour (rich in A) is removed, and liquid left
is richer in B, composition a3, vapour with a3
&
• Vapour removed, composition shifts to a4,
vapour composition at a4
&
• Composition of remaing liquid shifts to b as
more A is drawn off, and b.p. of liquid,
vapour becomes richer in B
• Finally, at composition b the vapour of A
has the same composition as the liquid
• Evaporation occurs without change in
composition, and the mixture is an
azeotrope (boiling without changing), &
distillation cannot separate the components