M-1403 J. Chetn. Thernwdwamics
1982, 14. 703.-706
The excess enthalpies of bicyclohexyl + a cycloalkane n-alkane at two temperatures T.
M. LETCHER
and
+ an
and B. W. H. SCOONES
Department of Chemistry. Rhodes University. Grahamstow 6140. South Africa (Received 4 January 1982) The excess enthalpies of bicyclohexyl + cyclopentane. + cyclohexane. + cycloheptane. + n-hexane. + n-octane. and + n-decane have been measured over the whole composition and 298.2 K. The excess enthalpies of bicyclohexyl + n-hexadecane has also been measured 308.2 K.
+ cyclooctane. range at 288.2 at 298.2 and at
1. Introduction The molar excessvolumes for bicyclohexyl + a cycloalkane and + an n-alkane have recently been reported by the author. (‘-3’ Here we report the molar excessenthalpies for most of the above mixtures at 298.2 and 2X8.2 or 308.2 K.
2. Experimental The purities of the hydrocarbons used in this work are given in table 1. together with the suppliers of the hydrocarbons. The purity was determined by g.1.c. as previously described.“,2’ In most cases the supplied hydrocarbon had an estimated purity greater than 99.2 moles per cent. As a result only the n-octane, cycloheptane. and IIhexadecane were further purified. The first two were purified by careful distillation while the n-hexadecane was purified by fractional crystallization followed by distillation. The Hz measurements were determined using a commercial L.K.B. 2107 calorimeter. Our calorimeter was fitted with a calibrated ammeter so that the current through the heater could be more accurately determined. The temperature of the TABLE Liquid
102x
cyclopentane cyclohexane cycloheptane cyclooctane n-hexane
99.3 99.5 99.5 99.2 99.2
0021 43
9614’82’080703+04
1, Hydrocarbon
suppliers
and estimated
Supplier Aldrich Riedel de Hahn Merck-Schuchardt PfaLtZ and Brauer British Drug Houses $02.00/O
mole-fraction
Liquid
10ZX _----.. -___
n-octane n-dodecane n-hexadecane bicyclohexyl
(
purities
1982 Academic
99.6 99.2 99.1 99.2
x
---
Supplier
Merck-Schuchardt British Drug Houses Merck-Schuchardt Aldrich
Press Inc. (London)
Lrmited
T. M.
704 TABLE
LETCHER
AND
B. W. H. SCOONES
2. Molar excess enthalpies Hk for xC,~H,, C,.H,, and the deviations 6Hz calculated from
(bicyclohexyl) + (1 -.x)C,H,,+, equation (I) and the coeflicients
and + (1 of table 3
Y)P
&HIm J.mol
’
C,H,, 288.2
298.2
0.1017 0.1543 0.3477 0.0735 0.1953 0.3007
17.2 25.4 33.0 10.0 17.9 23.2
-0.7 1.3 PO.2 0.3 - 1.5 0.1
0.4146 0.4876 0.5478 0.3975 0.4811 0.5426
0.0836 0.2526 0.3405 0.1117 0.2278 0.3491
16.4 39.2 46.0 19.6 31.8 38.5
-0.3 0.2 1.5 -0.6 0.3 1.5
0.4637 0.5514 0.6938 0.4469 0.4625 0.5630
0.2394 0.3410 0.4181 0.0915 0.1614 0.3137
52.8 72.9 80.6 20.8 33.9 56.8
- 1.5 2.2 1.3 -0.1 -0.4 1.4
0.5433 0.6478 0.7502 0.4562 0.5655 0.6273
0.0579 0.1959 0.3651 0.4975 0.1016 0.1911 0.3042
25.9 75.2 119.5 127.8 24.0 43.1 66.4
0.0 - 0.9 4.1 -0.1 0.4 -1.0 -0.1
0.5285 0.6077 0.6814 0.7615 0.4474 0.5206 0.6117
0.1115 0.1821 0.2228 0.0795 0.1391 0.1475 0.2525
-60.3 - 89.5 - 102.7 -44.2 -78.8 - 80.6 - 115.6
1.1 -1.0 -2.0 2.7 -3.7 -2.0 -2.0
0.3362 0.4446 0.6090 0.3407 0.3826 0.4852 0.5812
0.0715 0.1154 0.2683 0.0973 0.1546 0.2734 0.3361
41.2 60.3 108.2 46.3 67.8 99.1 108.2
0.6 -0.8 - 1.3 -2.9 0.0 0.1 PO.3
0.3915 0.4462 0.5831 0.4108 0.5005 0.5736 0.6992
33.0 30.8 28.1 23.9 22.2 20.3
-0.1 0.0 -0.4 0.5 0.1 0.0
0.6722 0.8317
21.8 12.2
-- 0.2 0.1
0.6337 0.8550 0.8739
17.5 6.9 6.0
0.4 0.0 -0.1
46.2 41.8 29.4 37.2 36.2 33.1
0.5 -0.5 -2.2 1.7 0.5 PO.1
0.7764 0.8531
22.5 15.6
-0.4 0.9
0.8635 0.9226
11.5 7.2
PO.2 0.5
84.1 79.8 68.3 65.7 65.3 61.0
PO.8 - 1.2 0.3 1.1 0.8 -0.6
0.9003
34.4
0.2
0.7104 0.7995 0.9136
53.2 41.3 22.0
- 1.3 - 1.5 0.7
128.0 122.6 113.5 101.5 84.2 87.4 86.3
-0.4 -2.6 -2.8 1.9 -0.2 -0.2 0.9
0.8369 0.9478
77.7 28.5
1.2 -0.2
0.7532 0.8265
68.4 51.0
0.8 -0.7
122.9 131.6 124.9 129.2 135.3 142.6 135.8
0.4 0.8 1.5 2.7 2.0 0.0 1.8
124.7 126.0 116.2 114.9 113.2 107.0 86.2
-0.3 0.0 1.3 0.5 -0.3 -0.2 0.0
C,H,, 288.2
298.2
C, zH,, 288.2
298.2
C,,H,, 298.2
308.2
288.2
298.2
-
0.7982 0.8583
-90.8 -68.7
~ 1.4 0.4
0.7014 0.8003 0.9481
- 118.5 -92.5 - 28.7
-0.1 - 1.4 0.1
0.6133 0.7415 0.8736 0.8054 0.8763
110.9 82.3 42.9 60.5 39.5
0.8 0.1 -0.3 0.3 -0.1
GHIZ 288.2
298.2
HF, OF
BICYCLOHEXYL
+ A CYCLOALKANE TABLE
T K
I
HF; J,mol-’
@f: J.mol-’
Y
AND
+ AN
705
n-ALKANE
2---conrinued
H;
----J.molfi
&Hi
---J.rnol-’
x
HZ
-__ J~mol~’
dHf.
--.--J,mol
I
C,H,, 288.2
298.2
0.0754 0.1776 0.2741 0.0682 0.1697 0.2938
58.3 112.6 143.5 45.9 95.5 127.8
0.2 -0.5 -0.5 0.4 -0.1 -3.7
0.3876 0.5009 0.6540 0.4007 0.4549 0.5331
0.0799 0.1923 0.2941 0.0436 0.1791 0.3070 0.4122
64.2 126.1 164.0 36.4 115.0 154.7 163.3
0.4 - 1.5 1.1 0.3 - 1.1 -0.6 - 3.4
0.4165 0.5364 0.6876 0.5282 0.5556 0.6285 0.7316
158.4 154.7 127.X 145.1 144.3 136.5
- 0. I 0.5 2.2 1.8 1.0 -0.6
0.7611 0.8197
91.3 74.4
2.6 0.8
0.6636 0.7581 0.9003
114.3 88.1 38.2
1.0 0.7 -. 0.4
177.8 178.2 146.0 162.9 159.0 147.5 119.2
- 2.8 2.2 2.3 0.9 0.5 2.0 1.1
0.8054 0.8735
98.4 70.2
- 2.3 0.5
0.8815 0.9258
62.2 38.4
I .4 .I 3
C,H,, 288.2
298.2
mixing cell was monitored using a calibrated thermocouple placed against the cell. L.K.B. Varioperpex peristaltic pumps were used to pump the liquids. The technique used in the measurementshas been described.‘4.‘) In all casesdegassedliquids were initially used but only for mixtures containing trhexane. cyclopentane, and cyclohexane did the results differ from those obtained from non-degassed liquids. When non-degassed liquids were used, air bubbles were released into the line on mixing. As a result degassed liquids were used for measurements on n-hexane + cyclohexane. bicyclohexyl + n-hexane, + cyclopentane and + cyclohexane. The technique and calibrations were periodically checked by determining Hz for the well documented n-hexane + cyclohexane at various temperatures. The results were always within 3 J. mol-’ of the results reported by Ewing and Marsh.16’
3. Results The Hk results are given in table 2 together with deviations 6HL calculated from the smoothing equation : n
GHk/(J.mol-‘)
= Hz/(J.mol-‘)-x(1
-x)
i A,(1 -2x)‘. r-o
(1)
where .Ydenotes the mole fraction. The coefficients A, are given in table 3.
4. Discussion The Hz for bicyclohexyl + cyclohexane has been previously reported by Lal and Swinton.“) Our results are within 2 J .mol~’ of their results over the whole
706 TABLE
T. M. 3.
Smoothing
Hydrocarbon
T/K
Cd,, C,H,, C,,H,, C,,H.s, ‘.-C,H,o PC,H,~ c-C,H,, c,-C,H,,
288.2 288.2 288.2 298.2 288.2 288.2 288.2 288.2
-.._-~
coefficients
Au 121.9 178.6 336.9 512.0 -531.9 495.3 617.2 717.9
LETCHER rl,
.4 L 72.2 68.9 -66.1 ~ 58.7 27.6 q36.4 215.8 145.7
ANI)
H. W.
for .vC,,H~~ tempemture A2 26.9 -26.3 -15.1 19.4 - 110.6 -2X.4 44.3 37.7
H. SCOONFS
+ (I--\)C,H,,, 7‘ 7:iK 29R.3 298.2 298.2 308.2 298.2 298.2 298.2 298.2
2 :md
+ 11
41 86.3 143.0 261.1 348.7 - 569.1 454.2 562.4 658.4
\N’,H,,
‘I 1
AL 52.3 63.0 ~ 10.4 ~ 61 .X ~ 35.5 104.7 170.x 157.3
14.4 5.2 -0.7 -65.9 - 59.6 - 17.0 1.9 72.9
composition range. The only other of our mixtures for which Hk has been published is bicyclohexyl + tt-dodecane. Some of our results are as much as 9 J. mol-* lower than the curve obtained by Jessup and Stanley’R’ from four points. The HE's for bicyclohexyl + cyclopentane do not fit into the pattern set by the other cycloalkanes. Although the trend is for Hi to increase with increasing size of cycloalkane, the Hi for the cyclopentane is very much lower than that for the other cycloalkanes. This behaviour was also seen in the V, results reported earlier”.“’ and is probably due to the cyclopentane molecule being flat and smaller than the other cycloalkanes. The value of (aV,‘/aT), at x = 0.5 increases in magnitude with increasing size of the cycloalkane. For cyclopentane it is -0.9 J. Km’ .mol- ‘. for cyclohexane - 1.O J K - ’ . mol - ’ . for cycloheptane - 1.4 J . K ’ . mol - ’ . and for cyclooctane it is -1.5 J.K-‘.mol-‘. The Hi(.u=0.5) for the n-alkane mixtures also increases with increasing carbon number and the magnitude of (aVz@:leT), at s = 0.5 also increases with carbon number. For n-hexane it is -0.90 J. K - ’ . mol- ‘. for n-octane it is -0.90 J.K-’ ‘mol-‘. for n-dodecane it is - 1.9 J. Km’ .mol-‘. and for tz-hexadecane it is -4.0 J.K-‘-mol-‘. The authors wish to thank Miss D. Perkins for assistance in some of the more tedious work and also Rhodes University and the CSIR (South Africa) for financial assistance. REFERENCES 1. 2. 3. 4. 5.
Letcher. T. M. /. Chenr. Thermo&nomics 1979, Il. 1175. Letcher. T. M. J. Gent. Thermodynamics 1981, 13. 27. Letcher, T. M. J. Chem. Thermodvtamics 1982, 14. 189. Harsted. B. S.: Thomsen, E. S. J. Chem. Thermo~vnomics 1974, 6. 549. L.K.B. 2107 Flow Microcalorimeter Operation Manual 1 21071121 -E02. S -16125 Bromma1. Sweden. 6. Ewing. M. B.; Marsh. K. N. J. Chem. Thermodvmmics 1970. 2. 295. 7. Lal, M.; Swinton, F. L. Truns. Furu&y SM. 1967, 63. 1596. 8. Jessup. R. S.; Stanley. C. L. J. Chem. Eng. Datu 1961. 6. 368.
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