ESTIMATION OF HEAT OF MIXING OF NONPOLAR ORGANIC LIQUID MIXTURES

Abstract

The mechanism of heat of mixing of two nonpolar organic liquids A and B has been studied. Most liquids have their minimum volume at the melting point.
As the temperature is increased, the liquids expand by virtue of creating the free volume v_f Inside the liquids. Suppose liquid A has the free volume v_fA and B, v_fB. Here, let v_fA>v_fB. As the consequence of the mixing of A and B, v_fA and v_fB are shared by both at the contact surface [or mixed fraction, cf. J. Chem. Eng. Japan, 1, (2), 99 (1968)], which results in the expansion of B and the contraction of A. When they contract or expand, heat is evolved or absorbed. In this way, using excess volume data, V^E, specific heats and densities of pure liquids and the equation written below, heat of mixing can be predicted approximately. Of more than twenty nonpolar binary liquid mixtures predicted, part of them showed good agreement with the experimental excess enthalpy in the literature, while setting F_A≈F_B≈1 in the following equation. Others showed a regular relation of F_A and F_B, which are characteristic of a homologous binary series.
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where, H^E= excess entnalpy, V^E=Jixcess volume,
X_A, X_B=Mole fractions of A and B in a liquid mixture,
F_A, F_B=Factors characteristic of a homologous binary system and for particular homologous mixtures F_A≈F_B≈1.