thermodynamic properties of solutions of monochloro...

IBcU•• J01lJ'DaJ of ChemistryVol. 16A, November 1978, pp. 915-927

Thermodynamic Properties of Solutions of Monochloro-, Dichloro- &Trichloro-acetic Acids in Chloroform at 298 K

M. L. LAKHANPAL & H. G. MANDAL

Department of Chemistry, Panjab University. Chandigarh 160014

Received 5 December 1977; accepted 4 A P'-il 1978

The thermodynamic, excess thermOdynamic and partial molar thermodynamic propertiesof mixina of the solutions of chloroacetic acids in chloroform at 298 K have been reported anddiscussed. The values of TAS!: and TAS, suaaest that unlike aqueous solutions of these acids,the structural order of their solutions in chloroform increases in the order mcnochloro- > di-chloro- > trlcbloro-acetic acid, which has heen attributed to the relative ionization of cbloroacetic acids.

THERMODYNAMIC studies on aqueous solu-tions of chloroacetic acids, reported earlier",reveal that these solutions exhibit structural

order. The structural order increases graduallyfrom monochloro- to trichloro-acetic acids. Thermo-dynamic studies on the chloroacetic acids have beenextended to their solutions in chloroform which isnot an associated solvent like water. Enthalpies ofmixing of solutions of the chloroacetic acids inehloroforrn have already been reported-. In thepresent note, the a~tivity data along with t~evarious thermodynamIc and excess thermodynamicfunctions have been presented and discussed.

Materials and Methods

Monochloro-, dichloro-, trichloro-acetic acids andchloroform used were purified by methods reportedearlier+

The activities of these solutions have beencalculated from vapour pressure data measuredwith the help of a differential micrornanometers+, atdilute concentrations and using the modified oilme-rcurv manometer+ for dilute solutions and ordinarymanometer for relatively concentrated solutions.

Results and Discussion

Since the vapour pressures of the chlo~oaceticacids are not so insignificant as to be Ignored,the partial vapour pressure of the ~olvent ~sdetermined by the procedure adopted In an earliercommunication", The values of the vapour pressuresand activities of the solute and the solvent for thevarious solutions are reported in Table 1.

TTterm<>dynamic and excess therm<>dY1!a~ic 1»'.0-perlies - The values of enthalpy of mixmg, dis-cussed in an earlier communicationt, are reportedin Table 2, along with the values of t~e. f~ee energyof mixing (calculated from the activities of thecomponents) and the entropy of mixing. Thevalues of AG". for the systems are generally small

TABLE 1 - SOLUTION VAPOUR PRESSURES ANDACTIVITIES OF THE COMPONENTS OF CHLOROFORM

SOLUTIONS OF CHLOROACETIC ACIDS AT 298 K

Xl Soln vapour PI p. al O2pressure P (em) (em)

(cm)

MONOCHLOROACETIC ACID-CHLOROFORM SYSTEMS

0·9817 19·2388 19·2218 0·0170 0·9836 0·61730·9700 19·0461 19·0271 0·0190 0·9736 0·68990·9424 18·6634 18·6429 0·0205 0·9539 0·74440'9065 18·249 18·2265 0·0225 0·9326 0·81700·8713 17·806 17·7822 0·0238 0·9099 0·8640·8404 17·426 17·4015 0-0245 0·8904 0·8890·8161 17·067 17·0415 0·0255 0-8720 0·9260·7920 16·681 16·6545 0·0265 0-8522 0·9620·7577 0·8300· 1·000

DICHLOROACETIC ACID-CHLOROFORM SYSTEMS

0·9814 19·3111 19·3011 0·0100 0·9876 0·39810·9607 18·9865 18·9733 0·0131 0·9708 0'52230·9294 18·489 18·4746 0·0144 0·9453 0·5720·8475 18'139 18·1234 0·0156 0·9274 0·6220·8174 17·531 17·5147 0·0162 0·8962 0'6470·7134 16·302 16·2847 0·0172 0·8333 0·6870·5924 14·828 14·8099 0'0181 0·7578 0·7210·4401 13·743 13·7230 0·0200 0'7021 0·7960·2162 10'025 10·0022 0·0227 0·5118 0·9060'1453 7·054 7·0302 0'0237 0·3597 0·9450·0538 5·015 5·0805 0'0245 0·2599 0·975

TRICHLOROACETIC ACID-CHLOROFORM SYSTEMS

0·9853 19·3338 19·3275 0'0063 0'9890 0·42260·9686 19·1289 19·1209 0·0080 0·9784 0·54090·9434 18·8124 18·8027 0·0097 0·9621 0·65920·8979 18·129 18-1187 0·0102 0·9271 0·6930·8503 17·519 17·5084 0·0106 0·8960 0·7180-7616 16'499 16·4870 0·0120 0·8436 0·8110·6564 14·977 14·9645 0·0125 0·7657 0·8450'5833 13·998 13·9849 0·0131 0-7160 0·8870·5359 12·216 13-2022 0·0137 0·6755 0·9390·5027 12·815 12·8010 0-0140 0·6551 0-946

- 0·5009 0·6550· 1·000

·The extrapolated values of the activities al at saturationsolubility.

925

INDIAN J. CHEM., VOL. 16A, NOVEMBER 1978

TABLE 2 - THERMODYNAMIC AND EXCESS THERMODYNAMIC PROPERTIES OF MIXING FOR CHLOROFORM SOLUTIONSOFCHLOROACETIC ACIDS AT 298 K

X, llH", llG", TllS", ilG! Tt::.s! TllS!'(kJ/mol) (kJlmol) (kJ/mol) (kJ/mol) (kJ/mol) (kJ/mol)


0·9817 0·34 -0'06 0·40 0·16 0·17 -0'060·9700 0·55 -0·09 0·65 0·24 0·31 -0'080·9424 1·02 -0·15 H7 0·39 0·63 -0·130·9065 1-62 -0·20 1·82 0·57 1·05 -0,170·8713 2-18 -0·25 2-43 0,70 1·48 -0,200·8404 2·66 -0·29 2·95 0·80 1·86 -0·230·8161 3·01 -0·31 3·32 0·87 2-14 -0·260·7920 3·36 -0,33 3·69 0·93 2·42 -0,290·7577 3,80 -0'35 4015 1-02 2·78 -0·39


0·9814 0·02 -0,07 0·09 0·16 -0,13 -0,130·9607 0·03 -0·13 0,16 0·28 -0'24 -0·240·9294 0·03 -0,23 0·26 0·40 -0·37 -0·370·8475 0·01 -0·34 0·35 0·72 -0·71 -0·710·8174 0·02 -0·42 0·40 0·76 -0,78 -0·780·7134 -0,08 -0,59 0,51 0·90 -0,97 -0·970·5924 -0·09 -0·74 0'65 0·94 -1-02 -1'020·4401 0·07 -0,70 0·77 1·00 -0,93 -0·930,2162 0·01 -0'55 0·56 0,74 -0'73 ....:0·73

0·1453 0·01 -0·49 0·48 0·54 -0,56 -0'560·0538 0·02 -0·24 0·22 0·28 -0,30 -0'30


0·9853 0·18 -0'06 0·24 0·13 0,05 -0,04

0·9686 0·38 -0·10 0·48 0·25 0·13 -0,050·9434 0·67 -0·15 0·82 0·39 0,28 -0'060'8979 1·21 -0·26 1-47 0,56 0,66 0·050·8503 1·79 -0,35 2-14 0·69 HO 0·210·7616 2,85 -0·46 3-31 0·92 1·94 0·530·6564 4012 -0'58 4·70 1-02 3·10 1·080'5833 5·00 -0·61 5-61 1·08 3·92 1,46

0'5359 5,56 -0·60 6·16 HI 4·46 1·720·5027 5·94 -0,59 6·53 H2 4,82 1·880·5009 5·98 -0,53 6,51 1·19 4,79 1·72

as would be expected for system exhibiting positivedeviations from ideal behaviour (Table 1). Thehigher values of TI::..S",for solutions of monochloro-and trichloro-acetic acids, as compared with thosefor solutions of dichloroacetic acid are naturallydue to the fact that the former compounds aresolids and the latter' a liquid at this temperature.

The excess thermodynamic properties I::..G!andTt::..SE are also given in Table 2. The values of theexce;s free energy of mixing are invariably positivewhereas the excess entropies of mixing are positiveonly for monochloro- and trichloro-acetic acids andsignificantly negative for dichloroacetic acid. Theextent of randomization of these solutes in thesolutions could not be compared by the magnitudeof the values of TI::..S!, since monochloro- and tri-

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chloro-<l:ceticacid~ are .in different physical statesthan dichloroacetic acid. For a more rationalcomparison, the values of TASE calculated from. ...equation

TAS!' = TAS",(expl)-x2.I::..Ht+RT!:;x;lnx;= TI::..S!-x2·!::..Ht

are given in Table 2. It is seen that the valuesof AG! are of the same order of magnitude for thevarious systems. The values of TAS!' are negativeexcept for solutions of trichloroacetic acid athigher concentrations. The positive values of I::..GEand negative values of TAS;" suggest high degre:of .ordering of these solutions. The values of

E'TAS", for chloroform solutions are found to be less

LAKHANPAL & MANDAL: THERMODYNAMIC PROPERTIES OF CHLOROACETIC ACIDS IN CHCl3

TABLE 3 - PARTIAL MOLAR THERMODYNAMIC ANDEXCESS PARTIAL MOLAR THERMODYNAMIC PROPERTIES OF

MIXING FOR CHLOROFORM SOLUTIONS OFCHLOROACETIC ACIDS AT 298 K

t.fl1

(kJ/mol)

--Et.G1 T t.S1 t.G1(kJ Imol) (kJ Imol) (kJ Imol)

T6sf(kJ/mol)


0·98170·97000'94240·90650·87130'84Q40·81610'79200'7577

0·020·Q40·130·180·280·410'530·710·80

-0·Q4-0'07-0·12-0,17-0'23-0,29-0·34-0·40-0'46

0·060·110·250·350·510·700'871'111·26

0'0050'010·030·070'110'150'160'180·22

0'020·030·100·110·170'270·360'530'58


0·98140·96070·92940·84740·81740·71340·59240·44010·21620'14530·0538

0·010'020'04-0·100·120·02

-0'21-0,17

0'290·160·02

-0·03-0,07-0·14-0,19-0'27-0,45-0,69-0·88-1,66-2'53-3·34

0·Q40·090'180·290·390·470·480·711·952'693'36

0'010·030·Q40·220'230·380'611-162'142·253'95

-0,003-0'001-0,005-0,12-0,11-0·37-0·40-0'98-1'84-2·09-3,88


0'98530·96860'94340·89790·85030·76160'65640·58330'53590'50270'5009

0'020'050'060'08 .0·110·190·250·300·360·560·80

-0,03-0,05-0,09-0,19-0,27-0·42-0,66-0'83-0'97-1'05-1·05

( ·050·100'150·270·380'610·911'131'331·611'85

0'010·020·050·080'130·250·380·510·570'660'67

0'020·030'010'08

-0'01-0,06-0·13-0·20-0'21-0'09

0·14

negative as compared to those in aqueous solutions",This may be attributed to the fact that the effectof solvation of ionic species is much more pro-nounced in aqueous solutions than in solutions Inchloroform. Unlike the aqueous solutions thestructural order In chloroform solutions appearsto be monochloro- > dichloro- > trichloro. Thismay be explained by the fact that the degree ofionization of the acids increases in the ordermonochloro- < dichloro- < trichloroacetic acid.

The partial molar thermodynamic properties ofmixing (aRI, rss, and aG\) are reported in Table 3.The values of partial molar entropy Tb..S1 arepositive throughout. It is well known that chloro-acetic acids get dimerized In organic solvents.In spite of the increase in order brought about bythe dimerization of acid s in chloroform, the entropyeffects rss, are positive, which can be attributedto the decrease in the specific orientations of themolecules of chloroform in these solutions than inthe pure solvent.

Acknowledgement

One of the authors, H. G. Mandal, is thankfulto the CSIR, New Delhi, for financial assistance.

References1. LAKHANPAL, M. L., GURCHARAN LAL & MANDAL, H. G.,

Indian]. Chem., 14A (1976), 639.2. LAKHANPAL, M. L., AHUJA, S. C. & MANDAL, H. G ..

Indian ]. Chem., 13 (1975), 377.3. PUDDINGTON, 1. E., Can. J. Chem., B27 (1949), 151.4. LAKHANPAL, M. L., CHHINA, K. S. & SHARMA, S. C.,

Indian]. Chem., 6 (1968), 50S.5. LAKHANPAL, M. L., GURCHARAN LAL & MANDAL, H. G.,

Indian]. Chem., 11 (1973), 1186.6. MORRISON, R. T. & BOYD, R. N.. Organic chemistry

(Prentice-Hall, 'ew Delhi). 1969, 600.

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thermodynamic properties of solutions of monochloro...

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