Discussion around the paradigm of ideal mixtures with emphasis on the definition of the property changes on mixing

In this paper, the various concepts of ideal mixtures found in the open literature are analyzed and compared. It is in particular shown that expressions conventionally admitted for the ideal-mixture property changes on mixing are incorrect when the ideal mixture is obtained from pure components which are not in the same aggregation state as the mixture. Among these properties, a special attention is devoted to the ideal-mixture Gibbs energy change on mixing since it is used to determine the equilibrium conditions. After explaining how to properly estimate this quantity, it is shown how to correctly perform the double-tangent construction of coexisting phases for binary systems modeled with the gamma-phi approach.

► Analysis and comparison of the various concepts of ideal mixtures.
► The mixing enthalpy can be different from the excess enthalpy.
► Volume change can be observed on the formation of an ideal mixture.
► Correct expressions of the ideal-mixture property change on mixing.
► Usefulness of the double-tangent construction when the gamma-phi approach is used.