Distillation behavior – solutions that boil without composition change In vapor–liquid equilibrium, what are solutions called that distill (boil and condense) without any change in composition of the vapor and liquid phases?

Introduction / Context:
An azeotrope is a constant-boiling mixture whose vapor phase has the same composition as the liquid at a given pressure. Azeotropes are central in separation science because they impose limits on simple distillation and often necessitate entrainers or pressure-swing techniques.

Given Data / Assumptions:

• Binary or multicomponent liquid mixtures under a fixed pressure.
• Well-defined azeotropic composition at the specified pressure.

Concept / Approach:
At the azeotropic point, y_i = x_i for all key components, so the mixture boils at a constant temperature and composition. Simple batch or differential distillation cannot change the composition past this point, which defines a fundamental separation limit. Ideal, saturated, or supersaturated labels do not capture this constant-composition boiling behavior.

Step-by-Step Solution:

Verification / Alternative check:
Phase diagrams for ethanol–water show a minimum-boiling azeotrope near 95.6 wt% ethanol at 1 atm; the mixture distills without composition change at the azeotropic point.

Why Other Options Are Wrong:

• Ideal: Refers to Raoult's-law behavior, not constant-composition boiling.
• Saturated/supersaturated: Concern the amount dissolved, not VLE composition equality.

Common Pitfalls:
Assuming ideality implies no azeotrope; some near-ideal systems still exhibit weak azeotropy depending on non-ideality and pressure.

Final Answer:
azeotropic