What does azeotropic mean?
"Azeotropic" is a technical adjective used in chemistry to describe mixtures of liquids that behave in a strikingly uncooperative way: they boil at a constant temperature and vaporise in exactly the same proportions as the liquid itself. A mixture with this property is called an azeotrope, and because its vapour has the same composition as the liquid, conventional fractional distillation cannot separate it into its components. The classic example is the ethanol–water azeotrope at about 95% ethanol, which famously limits how concentrated alcohol can become by distillation alone. The word appears almost entirely within chemistry and chemical engineering — in phrases such as "azeotropic distillation" or "azeotropic mixture" — and carries no figurative or everyday use. It is valuable precisely because it names a real limit on one of science's oldest separation techniques, and overcoming azeotropic behaviour requires specialised methods such as adding an entrainer or using pressure-swing distillation.
adjectiveRelating to or being an azeotrope: a mixture of two or more liquids that boils at a constant temperature and distils without change in composition, behaving as if it were a single pure substance.
- (Of a liquid mixture) boiling at a constant temperature without change in composition; constituting or involving an azeotrope.
"The ethanol–water mixture forms an azeotropic system that cannot be fully separated by ordinary distillation."
"Because the ethanol–water system is azeotropic, repeated simple distillation cannot yield pure ethanol."
"Chemical engineers often add an entrainer to break an azeotropic mixture so its components can be separated."
An azeotropic mixture breaks the rules of distillation: it boils like a single pure liquid and simply refuses to be separated further.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of azeotropic
"Azeotropic" derives from "azeotrope", coined in the early twentieth century from Greek elements: the privative prefix a- ("not"), zein ("to boil"), and tropos ("turning, manner"). The coinage literally suggests something that does not change when boiled, capturing the defining property of these constant-boiling mixtures. It shares roots with other Greek-derived words such as "trope", "heliotrope", and "zoetrope", all built on tropos.
Related word forms
How azeotropic is actually used
Strictly technical vocabulary, confined to chemistry and chemical engineering registers. It functions almost exclusively attributively ("an azeotropic mixture", "azeotropic distillation") rather than predicatively.
Easily confused with azeotropic
"Azeotrope" is the noun denoting the constant-boiling mixture itself, while "azeotropic" is the adjective describing anything relating to such a mixture.