Excess volumes and excess heat capacities of tetrachloroethene + cyclohexane, + methylcyclohexane, + benzene, and + toluene at 298.15 K

M-1376 J. Chem. Thermo+tamics

1982, 14. 523-529

Excess volumes and excess heat capacities of tetrachloroethene + cyclohexane, + methylcyclohexane, + benzene, and + toluene at 298.15

K”

J.-P. E. GROLIER, A. INGLESE.” and EMMERICH WILHELM ’ Lahoratoire de Thermodynumique et Cinktique Chimique, UniversitP de Clermont II. F-631 70 AuhiPre, France (Received 27 October 19X1) Molar excess volumes V,” at 298.15 K were obtained. as a function of mole fraction x. for the four liquid mixtures tetrachloroethene + cyclohexane, + methylcyclohexane, + benzene. and + toluene from measurements of the density with a vibrating-tube densimeter. The excess volumes are positive in al1 cases, the largest value of V,” being found for (xC,CI,+ = 0.529 cm3 ‘mol-’ at .x = 0.4540. The maximum values (1 -x)c-C&L,,: : Pz(max) VE(max)/(cms ‘mol-‘) for the other mixtures, in the sequence given above. are: 0.180 at x = 0.4330,0.405 at x = 0.4538, and 0.131 at x = 0.4532. A Picker flow calorimeter was used to determine molar excess heat capacities at 298.15 K for each of these binaries: CF.,, is negative for all four. In the same sequence, CF,,(min)/(J’K-‘.mol-‘I is, respectively. - 1.41 at x = 0.5323. -0.92 at x = 0.4899. -2.25 at x = 0.4196. and -0.54 at x = 0.4056.

I. Introduction

Mixtures of aromatic hydrocarbons with halogen-containing aliphatic compounds years. have been investigated extensively during recent (i-lo’ In particular, results of thermodynamic and spectroscopic studies on mixtures of tetrachloromethane with various aromatic liquids have frequently been discussed in terms of specific interactions. such as charge transfer complexes or n -n. interactions.‘“-” Hence it seemed interesting to measure some thermodynamic quantities of tetrachloroethene (C2CI,) with benzene and toluene. Mixtures with cyclohexane and methylcyclohexane were included to provide a reference basis for which the absence of specific interactions of the type mentioned above may be safely assumed. Similarly to tetrachloromethane, C&l, does not exhibit conformational equilibria as, for instance, do 1,2-dichloroethane or 1,1,2,2-tetrachloroethane, and it has no permanent dipole moment. In this paper. we report molar excess volumes V,E and ’ Communicated in part at the Journ& A.F.C.A.T.. Barcelona. Spain. 4 to 6 June 1980. b On leave from Istituto di Chimica Fisica, Universita di Bari. Via Amendola 175. Bari, Italy. ’ On leave from Institut fur Physikalische Chemie. Universitat Wien, Wahringerstrage 42, A-1090 Austria.

002lL9614/82/060523+07

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C 1982 Academic

Press Inc. (London)

Wien.

Limited

524

J.-P. E. GROLIER.

A. INGLESE,

AND E. WILHELM

molar excess heat capacities Cz,,,, as a function of mole fraction, for tetrachloroethene + benzene (C,H,), + toluene (C,H,CH,), + cyclohexane (c-C,H,,). and + methylcyclohexane (c-&H,,CH,) at 298.15 K.

2. Experimental All liquids were puriss. grade from Fluka, with stated purity Z 99 moles per cent for C2Cl,, and purity > 99.5 moles per cent for the hydrocarbons. They were carefully dried with molecular sieve and used without further purification. Binary mixtures were prepared by mass. The possible error in the mole fractions is estimated to be less than 10-4. As previously, (9*19,“) densities p were measured with a vibrating-tube densimeter from Sodev (model 02D), operated under flow conditions. The instrument was calibrated with doubly distilled and degassed water,“l’ and dry nitrogen at atmospheric pressure. Molar excess volumes were determined according to v,” = V,-{xV,+(l-x)VZ;

= xM,(p,‘-p;‘)+(l-x)M,(p,‘-p;‘).

(1)

Here v, Mi, and pi denote, respectively, the molar volume, the molar mass, and the density of tetrachloroethene (i = I), of aromatic hydrocarbon or cycloalkane (i = 2) and of mixture (i = m); x is the mole fraction of C$l,. Heat capacities per unit volume C,/V were determined with a Picker flow calorimeter(10~‘9~20*22~23’ from Setaram, using the stepwise procedure. For all measurements we used a temperature increment of approximately 1 K centred on 298.15 K. Molar excess heat capacities were calculated from c,“.m = C,,,-~xC,.1+(1-x)C,,*~.

;

(2)

where C,, with the appropriate subscript, is the molar heat capacity at constant pressure of pure component i or mixture m. For both densimeter and calorimeter, temperature control by the thermostats was better than + 0.003 K, as checked by a quartz thermometer (Hewlett-Packard, model 2801 A). The maximum inaccuracy of the temperature readings is estimated to be less than f0.005 K. TABLE 1. Density p and moIar heat capacity at constant pressure C,,, of the pure Iiquids at 298.15 K

This work

C,Cl, C-CsH,,

c-C,H, ICH, C6H6

Cd-W-f,

d(kg.m-7 Literature

1614.1 1614.5,@4’ 1614.32’25’ 773.8 773.89’*@ 765.0 765.06’=’ 873.6 873.70’26’ 862.2 862.31 lz6’

This work 146.49 156.45 185.29 135.72 157.01

C,,/(J,K-‘.mol-‘) Literature 141.0” 156.75:“’ 184.54!29’ 136.00,‘= 157.26/= 157.03!23’

156.07:“’ 185.12:3”’ 135.76:=’ 157.11:30’ 156.94”

156.35!“’ 156.41”” 184.84!31’ 184.75 “” 135.61”” 156.99,‘3”

’ Calculated from an equation for C,,, as function of temperature given in reference 26, table 2.11. p. 45.

V,” AND C;.m FOR TETRACHLOROETHENE

525

+ HYDROCARBON

3. Results and discussion Experimental densities and heat capacities of the pure liquids are summarized in table 1. In general, agreement with literature data is satisfactory. However, there appear to exist no reliable recent heat-capacity measurements for tetrachloroethene. Results for the mixtures, that is V,” and C,“,,, are contained in table 2, and are plotted against mole fraction x of C,Cl, in figures 1 and 2, respectively. For each mixture, the excess quantities Q” = V,“/(cm” .mol-‘) or Q” = CF,,/(J.K-’ .moll’) were fitted to a smoothing function: Q” = x(1 -x)

C 4,(2x-l)‘,

(3)

i=O

TABLE 2. Molar excess volumes V,” and molar excess heat capacities C,“,,, as functions of the mole fraction x for xC,Cl, + (1 -x)c-C~H,~, + (1 -x)c-C,H,,CH,. + (1 -x)&He. and + (1 -x)&H&H3 at 298.15 K X

v,”

cm3.mol-’

CEp.m

J.K-‘,mol-’

X

-m

P

cmJ.mol-’

C,“.m

J.K-‘.moI-’

X

c

cm3.mol-’

c;.rn

J,K-‘.mol-’

0.1163 0.2350 0.3201

0.2498 0.4133 0.4878

- 0.447 - 0.893 - 1.124

xC,Cl, + (1 -x)c-&Hi2 -1.346 0.4319 0.5292 0.5060 0.5248 -1.413 0.6068 0.4799 -1.371

0.6846 0.7833 0.8636

0.4214 0.3197 0.2163

- 1.236 - 0.982 - 0.695

0.0720 0.2423 0.2809

0.0582 0.1484 0.1608

-0.244 - 0.678 - 0.758

xC,CI, 0.3982 0.5117 0.5690

0.6731 0.7916 0.8497

0.1401 0.0964 0.0728

- 0.774 -0.603 - 0.465

0.1455 0.2332 0.3641

0.2304 0.3159 0.3934

- 1.412 - 1.882 - 2.203

0.4322 0.5478 0.6444

0.7128 0.8282

0.3031 0.2068

- 1.607 - 1.042

0.1380 0.2307 0.3144

0.0712 0.1022 0.1202

- 0.334 - 0.457 -0.517

xC,C14 + (1 -x)C,H,CH, 0.4362 0.1296 - 0.524 - 0.503 0.5092 0.1293 0.5915 0.1217 - 0.459

0.6779 0.7730 0.8677

0.1062 0.0818 0.0512

-0.384 - 0.287 -0.173

+ (1 -x)c-C,H,,CH, -0.899 0.1783 0.1736 - 0.937 -0.866 0.1674

xC2CI, + (1 - x)C,H, 0.4053 -2.120 0.3912 0.3500 - 1.863

by the method of least squares with all points weighted equally. The n coefficients Ai and the corresponding standard deviations o(Q”) are given in table 3. These coefficients were used to obtain the calculated solid curves in the figures. The excess volumes are positive for all mixtures, and rather symmetric. No literature results for V,” at 298.15 K could be found for any one of these systems. However, the measurements of Nath and his colleagues.‘6,7’ on three of them at 293.15 and 303.15 K allow interpolation to 298.15 K: I/,E(x=0.5)/(cm3~mol-‘) is, respectively, 0.490 for (&CL, + +c-C,H,,), 0.373 for (+C2Cl, + +C,H,), and 0.109 for (jC,Cl, + &H&H,). Their results are all considerably smaller than ours with deviations (at x = 0.5) as large as 0.035 cm3 . mall ’ (for &&Cl, + ;Sc-C,H, 2), which

526

J.-P. 0.6

I

E. GROLIER, I

A. INGLESE. I

AND 1

I

E. WILHELM I

I

I

!

0 0

0.2

0.4

0.6

0.8

1

x FIGURE (1 -xk-C&I,)) (1 -x)C,H,CH,j

1. Molar excess volumes V,” at ; 0. {xc,% + (1 -xk-C,H,&H,; The curves have been calculated

298.15 K. Experimental results: 0, {XC&~,+ ; 0, jxC,Cl~ + (1 -x)C,H,) ; n , {xc& from equation (3) with coefficients from table 3.

+

-2

0

0.2

0.4

0.6

0.8

1

X

FIGURE 2. Molar excess heat capacities C,“.m at constant pressure at 298.15 K. Experimental results: 0, {xC2C14 + (1 -x)c-C~H,~) ; 0. (xC,CI,+ (1 -~)c-C,H,,CHJ; ; 0, (xC2CI, + (1 -x)C,H,; ; n , {xCzCI, + (1 -x)&H&H,). The curves have been calculated from equation (3) with coefficients from table 3.

V, AND C;,m FOR TETRACHLOROETHENE

+ HYDROCARBON

527

TABLE 3. Coefficients Ai and standard deviations a(QE) for least-squares representation by equation (3) of V~andC~,,forxC,CI,+(l-x)c-C,H,,. +(l -x)c-C,H,,CH,, +(1-x)&H,. and +(l -xlChH,CH, at 298.15 K

Al

QE xC,CI, t- (1 -x)c-C,H,~ t (l-x)c-C,H,,CH, t (1 -x)C,H, + (1 -x)C6H,CH,

V,E/(cd mol 1) CE.m/(J.K-l.molm’) V~/crn’m~l-~)

2.0981 -5.606 0.7050 - 3.663 1.6075 - 8.785 0.5200 - 2.067

-0.3913 - 0.845 -0.1996 0.148 - 0.2944 2.724 -0.1000 0.874

0.0253 0.862 ...-. 0.0573 - 1.030 -.

0.0017 0.012 0.0009 0.018 0.0021 0.017 0.0007 0.009

is definitely outside our experimental accuracy, (9. lo’ Gracia et u/.“.~’ have measured V,” at 303.15 K for tetrachloroethene -I- cyclohexane and + benzene. Using the same temperature dependence of V,” as above, (6.7) their measurements yield the following ‘values at 298.15 K: V,“(x = 0.5) = 0.511 cm3.mol-’ for (&Cl, + fc-ChH12). much closer to our result and V,“(x = 0.5) = 0.399 cm3.mol-’ for (+jC,Cl, + +C,H,). in good agreement with our value. For C,“,,, no literature data could be found for comparison. Though a detailed discussion in terms of heat capacities at constant volume and isothermal compressibilities@. lo* “. “. 34*35’ is deferred until thermal expansivities and ultrasonic speeds are available for these mixtures, a few comments are indicated (in the following all quantities refer to 298.15 K). The molar volumes of Ccl, and C&l, are almost equal (within about 5 per cent); however, the volumetric behaviour of systems formed by mixing them each with either cyclohexane or benzene is remarkably different: V,“(x = 0.5)/(cm3 .mol-‘) = 0.165 for (fCC1, + $PC~H~~),(~‘~) 0.525 for ($CZC14 + +c-C6H12), 0.005 for (*Ccl, -I-+C~H~).(~” and 0.402 for (+C&l, + &,H,). The same trend, that is to say more positive excess volumes for the mixtures with C&l, as compared to those with Ccl,, can also be seen for mixtures with cyclopentane,‘25*38.39) t h us supporting the suggestion that the slightly smaller quasi-spherical tetrachloromethane molecules can be packed more closely with these cyclic hydrocarbons. We also note the smaller V,” for ($C,Cl, + 4c-C6H, ,CH3) and (fC2Cl4 + jC,H,CH,) as compared with the corresponding mixtures with the parent compounds cyclohexane and benzene. The influence of methyl groups attached to cycloalkanes upon V,” (packing effect) has recently been investigated by Kohler et u1.(39~40’ For (fC&l, + $C,H,) the molar excess enthalpyt Hi(x = 0.5) = 516 J’mol -I. which value is more positive by about 400 J. mol-’ than that for (41) The corresponding value for (&2Cl4 + +c-C,Hr Z) (see WC14 + fC,H,). footnote) is 466 J.mol-‘. and for (*Ccl, + Jc-C6HI 2)(42’ is HE@= 0.5) = 166 J.mol-‘. CE,, for (+C,Cl, + +C6H6) is rather strongly negative : CF,,(x=O.5)= -2.20 J.K-‘.mol-‘, in contrast to the result for t Adjusted to 298.15 K by utilizing results at 303.15 K”’ and f$,, of this work

528

J.-P. E. GROLIER,

A. INGLESE.

AND E. WILHELM

(+CCl, + &Hs):iO’ i.r. 1.17 J.K~‘.moll’. It is more negative than for (fC&l,++c-C,Hi2), for which CF,,(.u=O.5)=-1.40 J.K-‘~moll’. For ($C,Cl, + &&H&H,). C,“,,(x = 0.5) = - 0.52 J K - ’ mol ‘. as compared with 1.39 J.K-’ .moll’ for (fCC1, + QC6H,CH3),‘5’ and -0.92 J.K- ’ .moll’ for ($C,Cl, + +c-CeH, iCH,). For comparison we also present the corresponding excess quantities of(+(CH,),CHCH(CH,), + $C,H,j :(43.44) V,” = 0.330 cm’.moll’, HE = 913 J.moll’, and CF.,, = -2.96 J.K~‘.moll’. In summary, the mixtures {xC,Cl, + (1 - x)CgH6) and ; xC,Cl, + (1 -x)C,H,CH3) behave in a way reminiscent of “regular” mixtures of two nonpolar liquids,‘45’ .m support of the conclusions drawn by Gracia et LX/.(‘) However, as demonstrated by McGlashan and his colleagues,‘16-‘8’ care must be exercised in drawing such conclusions, and hence these mixtures should also be studied spectrophotometrically.‘4”’ Financial support within the frame of the Austrian-French technical cooperation is gratefully acknowledged by E.W.

treaty on scientific and

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+ HYDROCARBON

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