Combinatorial Entropy of Mixing for Molecules Differing in Size and Shape

In reducing experimental vapour–liquid equilibrium data it is common to calculate the Gibbs energy of mixing in excess of that for a solution whose entropy of mixing is given by one of two expressions; ideal entropy or Flory–Huggins entropy. The first of these is proper for a mixture of small molecules of similar size and the second one is proper for a mixture of monomer and chain polymer. This paper considers intermediate cases where there are significant differences in molecular shape as well as size. An expression is derived for the combinatorial entropy of mixing; this expression has Flory's result as the leading term but also contains corrections for molecular bulkiness. The combinatorial entropy of mixing depends on characteristic parameters reflecting both molecular size and shape. Methods are given for simple evaluation of these parameters and illustrations for representative mixtures are presented. In some case, the corrections for bulkiness can be very large.

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Activities of Components in the Ca2MgSi2O7-CaSiO3Molten System

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19960837 ◽

1996 ◽

Vol 61 (6) ◽

pp. 837-843

Author(s):

Ladislav Kosa ◽

Ivan Nerád ◽

Katarína Adamkovičová ◽

Jozef Strečko ◽

Ivo Proks

Keyword(s):

Gibbs Energy ◽

Molar Mass ◽

Excess Entropy ◽

Enthalpy Of Mixing ◽

Real Particle ◽

Entropy Of Mixing ◽

Energy Of Mixing ◽

Gibbs Energy Of Mixing

Activities of the components, the Gibbs energy of mixing, and the excess entropy of mixing have been calculated for the Ca2MgSi2O7-CaSiO3 system. The mole fractions of the components were calculated assuming that in the point of the formal component Ca2MgSi2O7, the molar mass of the quasi-real particle in the melt corresponds to its formula molar mass, whereas in the point of the formal component CaSiO3 the molar mass of the quasi-real particle in the melt is 8.5 times higher than as corresponds to its formula. The fact that the enthalpy of mixing is zero whereas the excess entropy of mixing is non-zero suggests that Ca2MgSi2O7-CaSiO3 melts behave as athermal solutions.

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Thermodynamic Assessment of the AF–CrF3 (A = Li, Na, K) and CrF2–CrF3 Systems

Thermo ◽

10.3390/thermo1020014 ◽

2021 ◽

Vol 1 (2) ◽

pp. 205-219

Author(s):

Thomas Dumaire ◽

Rudy J. M. Konings ◽

Anna Louise Smith

Keyword(s):

Molten Salt ◽

Binary Systems ◽

Thermodynamic Assessment ◽

Excess Properties ◽

Alkali Cations ◽

Reactor Technology ◽

Energy Of Mixing ◽

Equilibrium Data ◽

Gibbs Energy Of Mixing ◽

Corrosion Mechanisms

Understanding the corrosion mechanisms and the effect of corrosion products on the basic properties of the salt (e.g., melting point, heat capacity) is fundamental for the safety assessment and durability of molten salt reactor technology. This work focused on the thermodynamic assessment of the CrF2−CrF3 system and the binary systems of chromium trifluoride CrF3 with alkali fluorides (LiF, NaF, KF) using the CALPHAD (computer coupling of phase diagrams and thermochemistry) method. In this work, the modified quasi-chemical model in the quadruplet approximation was used to develop new thermodynamic modelling assessments of the binary solutions, which are highly relevant in assessing the corrosion process in molten salt reactors. The agreement between these assessments and the phase equilibrium data available in the literature is generally good. The excess properties (mixing enthalpies, entropies and Gibbs energies) calculated in this work are consistent with the expected behaviour of decreasing enthalpy and Gibbs energy of mixing with the increasing ionic radius of the alkali cations.

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