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Vapor pressure isotope effects in the benzene (B)–cyclohexane (C) system from 5 to 80 °C. I. The pure liquids B- d ,B- d 1, o r t h o -, m e t a -, and p a r a -B- d 2, B- d 6,C- d , and C- d 12. II. Excess free energies and isotope effects on excess free energies in the solutions B- h 6/B- d 6, C- h 12/C- d 12, B- h 6/C- h 12, B- d 6/C- h …

1978; American Institute of Physics; Volume: 68; Issue: 7 Linguagem: Inglês

10.1063/1.436163

1520-9032

G. Jákli, P. Tzias, W. Alexander Van Hook,

Zeolite Catalysis and Synthesis

High precision measurements of the vapor pressure differences between some deuterated benzenes B-dx (x=1, para-2, and 6) and protio benzene B-d0; between para- and ortho-, and para- and meta-dideuterobenzene; and between perdeuterocyclohexane C-d12 and protiocyclohexane C-d0 were made from near the freezing point to the normal boiling point. The data are best represented as the logarithmic ratios ln R (d6) =ln (Pd0/Pd6) =1226.5/T2−12.178/T, ln R (para/ortho) =ln (Ppara-d2/Portho-d2) =2.6/T2, and ln R (para/meta) =ln (Ppara-d2/Pmeta-d2) =−2.0/T2, together with the deviations from the law of the mean Δ (d1) =6−[ln R (d6)/lnR (d1)]=0.177−3.6×10−4t and Δ (d2-para=3−[ln R (d6)/ln R (d2-para)]=0.028 +1.0×10−4t. The isotope effects are inverse and display significant deviations from the law of the mean. The cyclohexane results are given by ln R (C-d12) =−2188.4/T2−18.587/T. New measurements of the vapor pressures of benzene–cyclohexane solutions are also reported between 5 and 80 °C. The data are in good agreement with the best earlier work. Excess free energies of the equimolar solutions B-h6/B-d6 and C-h12/C-d12 have been measured between 20 and 80 °C. Suitable fits to the data yield the following results (30 °C); Gex(B-h/B-d), Gex(C-h/C-d); Hex(B-h/B-d), Hex(C-h/C-d); 0.57,1.04;1.1,3.1 J/mole. For the isotope effects on the excess properties of benzene–cyclohexane solutions differential pressure measurements were taken as a function of temperature (20–80 °C) and concentration (XC=0.10, 0.25,0.50,0.70,0.75,0.85,0.90). The isotope effects on the excess properties at 25 °C are as follows: Gex(B-d/C-h) −Gex(B-h/C-h), Gex(B-h/C-d)−Gex(B-h/C-h); Hex(-d/C-h)−Hex(B-h/C-h), Hex(B-h/C-d) −Hex(B-h/C-h); 7.5,2.6;32,0 J/mole at Xc=0.5, but equations are presented so that the effects can be calculated at any concentration or temperature. The results are briefly discussed in the context of the theory of isotope effects in condensed phase systems.