Mischverhalten

Mischverhalten describes how a mixture of substances behaves compared with an ideal mixture. In an ideal mixture, properties are predictable from the properties of the pure components, commonly assuming Raoult’s law or Henry’s law for vapor–liquid equilibria and additive volumes. Real mixtures often deviate from this ideal behavior, and such deviations are summarized as the mischenverhalten of the system.

In thermodynamics and solution chemistry, deviations are quantified by activity coefficients (gamma_i). The chemical potential of component i in a mixture is mu_i = mu_i^0 + RT ln(a_i), where a_i = gamma_i x_i. A zero excess Gibbs energy (G^E = 0) corresponds to ideal mixing; nonzero G^E characterizes Mischverhalten. Deviations can be negative or positive: attractive interactions between unlike molecules typically yield negative deviations (lower vapor pressure than ideal), while weaker or repulsive interactions yield positive deviations.

Several theoretical models describe Mischverhalten. The regular solution model provides a simple framework for non-ideal liquids. More sophisticated correlations include Margules, Wilson, and the non-random two-liquid (NRTL) model, as well as the UNIQUAC model, which account for molecular size and energy interactions to predict activity coefficients and excess properties.

Applications of understanding Mischverhalten span chemical engineering, solvent design, polymer blends, and environmental modeling of multi-component systems. It informs process design (distillation, extraction), formulation science, and the interpretation of VLE and solubility data. Experimental data, such as activity coefficients and excess Gibbs energy, are used to parameterize models and to predict behavior of mixtures under varying temperatures and pressures.