zeotrope

Definition

(Adjective) A liquid mixture of two or more substances that differs in composition between the vapor state and the liquid state when distilled or partially evaporated under a certain pressure.
A liquid mixture that obeys Raoult's law.
(e.g.) Zeotropic refrigerants are blends that change volumetric composition and saturation temperature glide as they boil. In short, they will fractionate.