Azeotrope
Definition and meaning of Azeotrope in chemistry.
An azeotrope is a mixture of two or more liquids that boils at a constant temperature and composition, with the vapor produced having the same composition as the liquid. This property makes azeotropes impossible to separate by ordinary fractional distillation.
In more detail
Azeotropes occur when intermolecular forces between components deviate significantly from ideal solution behavior, creating a maximum or minimum in the vapor pressure curve. At the azeotropic point, further boiling cannot change the mixture's composition because the liquid and vapor compositions are identical. Positive azeotropes have a lower boiling point than either pure component, while negative azeotropes have a higher boiling point. This phenomenon is crucial in industrial separation processes and requires specialized techniques such as adding a third substance or using pressure-swing distillation to break the azeotropic bond.
Key facts
| Field | Physical Chemistry |
|---|---|
| Composition | Remains constant during boiling; vapor equals liquid composition |
| Common Example | Ethanol-water (95.6% EtOH) at 78.2°C |
| Types | Positive (minimum BP) and negative (maximum BP) azeotropes |
Ethanol and water form a positive azeotrope at 95.6% ethanol by weight, boiling at 78.2°C, lower than pure ethanol's 78.4°C. This is why fermented beverages cannot yield pure ethanol through simple distillation.
Frequently asked questions
Why can't you separate an azeotrope by distillation?
Because the vapor composition equals the liquid composition at the azeotropic point, distillation cannot change the mixture's composition, making further separation impossible.
What's the difference between positive and negative azeotropes?
Positive azeotropes boil below either pure component; negative azeotropes boil above. Both result from intermolecular force deviations, but in opposite directions.