Thermodynamic properties of mixtures of linear and branched alkanes with 1,2-dibromoethane and tetrahydronaphthalene. Part 2.—Free energies and entropies of mixing
- 1 January 1977
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics
- Vol. 73 (7) , 1838-1849
- https://doi.org/10.1039/f29777301838
Abstract
Free energies of mixing have been measured by light scattering on seventeen systems at 300 K and two systems at 308, 318 and 328 K. The mixtures were branched and linear alkanes, C6 to C16, with 1,2-dibromoethane (DBE) and tetrahydronaphthalene (THN). The three branched alkanes were 2,2,4-trimethylpentane (br-C8), 2,2,4,6,6-pentamethylheptane (br-C12) and 2,2,4,4,6,8,8-heptamethylnonane (br-C16). The Flory–Huggins combinatorial entropy is more appropriate than the regular solution entropy to calculate GE from ΔGM. For the linear alkanes, GE and TSE increase with chain length from 900 and 541 J mol–1(n-C6) to 1130 and 963 J mol–1(n-C16) for the DBE systems. GE is ∼150 J mol–1 higher with the br-alkanes. GE for THN is also higher for the branched alkanes but only ∼400 J mol–1. The higher TSE values for the linear alkanes are associated with the long chain disordering entropy which was calculated to be respectively 477, 403 and 292 J mol–1 for n-C16, n-C12 and n-C8. The value of TSE(disorder) appears to be >HE(disorder). However this better solvent quality may be because the linear alkane has, owing to its shape, a larger combinatorial entropy than the compact branched alkane of the same volume. The value of TSE(disorder) diminishes with temperature as HE(disorder). TSE(disorder) compares reasonably well with the values obtained by viscosities with SnBut4 as order breaker. The causes for the large values of TSE for DBE are undoubtedly the same as those for HE previously discussed in Part 1.Keywords
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