1960
GEORGESCATCHARD,
SCOTT
E. W O O D
Summary The vapor-liquid equilibrium pressures and compositions of benzene-methanol mixtures have been measured a t approximately each eighth mole fraction a t 35 and 55' and for approximately equimolal mi.xtures a t 25 and 45'. The densities have been determined a t 25'. The excess,change of the free energy, enthalpy, and entropy have been calculated and expressed
[CONTRIBUTION FROM THE
AND JOHN
M. MOCHEL
Vol. 68
analytically. The excess free energy change is positive over the entire range of composition and is quite symmetrical. The change of enthalpy is positive over the entire range of composition but is quite unsymmetrical, the maximum occurring a t a mole fraction of about 0.3 in methanol. The excess entropy change is positive for solutions hnve a mole fraction up to about 0.3 in methanol and then becomes negative. C.4MBRIDGE,
hf ASS.
RECEIVED MAY31, 1946
DEPARTMENT OF CHEMISTRY, MASSACHUSETTS INSTITUTE OF
TECHNOLOGY]
Vapor-Liquid Equilibrium. VII. Carbon Tetrachloride-Methanol Mixtures1 BY GEORGESCATCHARD,
SCOTT
E. I v 0 G D 2 AND
JOHN
&I. &10CHEL3
TABLE I The present paper continues the measurement of the vapor-liquid equilibrium of solutions of DENSITIES OF CARBON TETRACHLORIDE-METHANOL MIXmethanol with the non-polar substances previTURESAT25' ously studied. The purification of the carbon Q't fraet Mule fract. CHIOH CHIOH d 6 l0OV "/vO tetrachloride was carried out as described in paper 0.0000 0.0000 1.58452 ....... ..... IV4 of this series. The methanol was of the same ,0296 ,1276 1.53764 $0.00032 +O. 049 material used for the measurements on the ben.0640 ,2472 1.48731 + .00026 + .039 zene-methanol system, VI.s The vapor pressure .1326 .4233 1.39691 - .00015 - .021 of carbon tetrachloride agreed with the values .l736 .5022 1.34781 - .00035 - .047 calculated by the equation given in IV within the .2579 ,6252 1.25715 - .00076 - .095 experimental error. .2597 ,6274 1.25526 - .00071 - .089 Experimental .7523 .3874 1.13928 - .00144 - .164 The apparatus and procedure for the density.3927 .7564 1.13472 - .00138 - ,156 composition measurements were the same as de.5987 0 98697 - ,00126 - .124 .8775 scribed in VI.5 Due to the high molecular weight 1.0000 1.0000 0.78654 ....... ..... of carbon tetrachloride i t was found necessary to correct the observed weight of the component eighth mole fraction of the whole system a t 35 and first weighed in making up the solutions for the 5 5 O and for approximately equi-molal mixtures a t weight of the vapor displaced on addition of the 25 and 45', using the same apparatus and prosecond component. The results are shown in cedure described in the earlier papers.& As in the Table I in which are given the weight fraction and attain a steady state for those mixtures whose mole fraction of methanol, the observed density, mole fraction of methanol in the whole system was 6, defined by equation VI-2,6 and 100 VM/Vo. 0.125 and 0.25 due to the extreme sensitivity of The absolute values of P/ VO for this system are the boiling- point to the composition of the liquid somewhat larger in the methanol poor solutions and the extreme sensitivity of this composition and about five times larger in the methanol rich to the distribution of methanol in the various parts solutions than for the benzene-methanol system. of the equilibrium still. For these mixtures the The compositions of the vapor and liquid sam- pressure was adjusted to maintain the temperature ples in the vapor pressure measurements were de- within 0.05' of the desired temperature for a t least termined from their densities by Eq. VI-2, 6 a n hour. being read off from a large scale graph of the obThe excess change in the free energy on mixing served 6 quantities versus the density. a t constant pressure over that of an ideal soluThe vapor -liquid equilibrium measurements tion of the same concentration was calculated were made a t intervals of approximately one- from the observed vapor pressure and the equilibrium mole fractions of the vapor and liquid phases (1) Presented before the Division of Physical and Inorganic Chemistry of the American Chemical Society at Atlantic City, New Jerusing the equations given in VI. The vapor pressey, April 10, 1946. sures of carbon tetrachloride in mm. used in these (2) Present address: Yale University, New Haven, Connecticut. calculations are 113.88, 174.47, 258.94 and 373.53 (9) Present address: Corninn Glass Works, Corning. New York. .~. -. a t 25, 35, 45 and 55', respectively. The limits a t (4) G. Scatchard, S. E. Wood and J. M. Mochel, THIS JOURNAL, 61, 3206 (1939). zero pressure of the difference between the molal (5) G. Scatchard, S. E. Wood and J. M. Mochel, ibid., 68, 1957 volume of the vapor and that of a n ideal gas a t (1946). the same temperature and pressure are -2290, (6) Equation numbers beginning with VI refer to the preceding - 1992, - 1749 and - 1549 a t 25, 35, 45 and 55O, paper.
CARBON TETRACHLORIDE-METHANOL MIXTUREEQUILIBRIA
Oct., 1946
respectively. The molal volumes of the liquid were determined from the density equations given in the “International Critical Tables.” The analytical expression of these results led t o difficulties similar to those with the benzenemethanol syste:m, and they were met in the same way. The parameters determined for equation VI-9 are -66.55
Alllz
A.ila A1222
= 307.97 = 300.65
+ 1.224T + 0.215T
1961
300
(1) (2)
+ 0.365T
. 200
(3)
+-,-
The experimental measurements are given in Table I1 in the order of the mole fraction of methanol in the liquid phase, the mole fraction of methanol in the vapor phase, the vapor pressure of the solution in mm., and the excess change of the free energy on mixing in cal. per mole. Adjacent to the last three columns the deviations of the corresponding quantities, calculated by equations 3, 4 and 9 of paper VI and equations 1, 2 and 3 of this paper, are also listed.
2 &-
100
TABLE I1 VAPOR PRESSURE OF CARBON TETRACHLORIDE-METHANOL MIXTURES XCH~OH
YCH~OH
?ev. iny
0.0169 .0189 ,1349 .3560 .4776 .4939 .6557 .7912 .9120
0.3297 .3374 .4630 ,4915 .5030 .5056 .5302 .6792 .7024
$0.118 .112 ,027 ,007 .003 ,005 f .003 .004 .004
.0254 .0579 .I493 .a647 ,4898 .4946 .6448 .7903 .go87
.3619 .3639 .4981 .5284 .5431 .5438 .5686 .6187 .7337
4-0.087 - ,044 ,013 .003
.4880
.4838
-
.4866
,5231
+
+ -
+ + -
Press., mm. 350 259.13 262.31 315.12 324.64 325.71 325.71 323.81 312.61 277.37
Dev. in
P
+39.3 f39.0 6.5 2.1 1.0 - 2.0 0.2 1.4 1.8
-
-
+ +
3SQ 580.66 $68.9 591.16 -24.9 716.95 5.6 741.36 1.3 4- .002 745.60 4- 0 . 1 .002 743.72 -I- 0 . 2 ,001 744.54 0.8 ,005 724.28 f 2 . 6 f .004 658.37 2.2
FXE 34.90 39.51 187.52 309.71 320.87 319.92 279.62 202.46 98.80
Dev. in FXE
+ 7.7 + 9.2 $10.0 + 9.6 -
2.1
- 1.9
+ 0.4 + 0.8 + 0.4 +
+ +
5.6 46.46 104.32 4-15.9 202.21 f 7 . 2 320.67 0.2 331.22 .4 330.90 .4 205.74 4- . 4 213.21 .2 110.72 4- 2 . 1
.016 205.30
+ 7.3
312.91
- 4.8
459 .002 500.13
-
0 . 3 326.57
- 0.5
-
-
+ -
25a
+ -
The results a t 35” are shown in Fig. 1 in which the total pressure and partial pressures plotted against the mole fraction of the liquid phase are represented by circles and the total pressures plotted against the mole fraction of the vapor phase are represented b y the flagged circles. The solid lines give the corresponding calculated values and the dotted lines show the behavior of the system according to Raoult’s law. The smooth values of the excess change of the free energy on mixing a t 35*, the heat of mixing, and 308.16 times the excess change of the entrowv on mixing, all expressed in cal. per mole are giv’eh in Table 111. The uncertainty in FxEat half mole
0.25
Fig. l.-Vapor
0.50 0.75 XI. pressure vs. mole fraction for carbon tetrachloride-methanol at 35 ’.
fraction a t 35 and 55’ is estimated to be about 1 cal. This would cause uncertainties of about 0.1 cal. per deg. in SxEand about 31 to 33 eal. in TSxE and HX”. The uncertainties in these quantities for solutions richer in methanol are probably smaller than these estimates. It is for this reason that the values of the latter two quantities are given to 1 cal. in Table I11 and the deviations in FxElisted in Table I1 are given t o 0.1 cal. The change of the volume on mixing a t constant pressure is again quite small and consequently the difference in the change of the thermodynamic functions on mixing a t constant pressure and on mixing a t constant volume may be ne lected.’ However the values of 308.16 (SVE - S, ) and EVM - H P M are given in Table 111.
i
TABLE I11 SMOOTH VALUESOF THE THERMODYNAMIC FUNCTIONS IN CAL. 308.16 z1
FxasE
HxM
0.1 .2 .3
140 235 293 320 321 300 258 195 110
102 169 200 200 174 130 77 28 -3
.4 .5 .6 .7 .8 .9
(7) G . Scatchard, T
308.16SxE
-
37 66 92 -120 -147 -171 -181 -168 -114
(SvE-SpE)EvM-HpM
-3 -3 -2
+8
-3 -3 -2 +1 +2 +5 +7 +7
+5
+5
+l
+2 +6 +7
~ Faraday ~ SOC., ~ 88, ~ 160 . (1937).
GEORGESCATCHARD. SCOTTE. WOODAND JOHN M. MOCHEL
1962
I
0.26
0.50
0.75
si. Fig. 2 .
--\'arioii4
tlicriiiutlyiiaiiiic fuiictioiis for carbon
tt tracliloricle-methanol at 35 '.
The smoutlicd values of FxEand TSXEa t 35' and Hxsfare shown in Fig. 2. The excess change of the free energy on mixing is positive over the whole range of composition and is fairly symmetrical. The heat of mixing is quite unsymmetrical and apparently becomes negative in the solutions
extrcmely ric:i in methanol. The minimum value is about - i cal. per mole which may be about thc. uncertainty in this range of cornposition.
'l'imofeev5 has reported positive and negative values of the heat of mixing. Further the simple inr.asurernents of the beat of mixing of carbon tetrachloride and ethanol reported by Scatchard and Raymondg indicate both positive and negative v:tlucs. It is therefore believed that although the uiicertai~itiesin the heat of mixing are somewhat largc tlie gericrd behavior is tliat shown by tile curve. 'i'he excc'ss cliatige o f tlie entropy 011 riiixing appears to be negative over the whole range oi composition, though much less so in the methanol pour solutions than in the methanol rich.
Discussion 'The unusual behavior of the ethanol-chloroform system was attributed9to the interactions between the hydrogens of the hydroxyl and of chloroform with the oxygen of ethanol and the chlorine of chloroiorni. 'l'hc 1)ositiw:enthalpy and excess eiitt-c)Ij\ (11' t[iiyiiig. i r i
