Possible Existence of a Negative (Positive) Homogeneous Azeotrope When the Binary Mixture Exhibits Positive (Negative) Deviations from Ideal Solution Behavior (That is, When gE is Positive (Negative))

The objective of this note is to give proof that the existence of a positive (or, respectively, negative) homogeneous azeotrope is not linked to the sign (positive or negative) of the molar excess Gibbs energy function ( g E ) but rather to the curvature of g E . We demonstrate that when g E is concave (or, respectively, convex), a binary system may exhibit a positive (or, respectively, negative) azeotrope. Because a concave or convex function may indifferently be positive or negative, when g E is positive (or, respectively, negative), a binary system may exhibit a negative (or, respectively, positive) azeotrope.