study of formamide + ethanol binary mixtures at various temperatures

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$751-757 Thermdynamic study f frmamide + ethanl binary mixtures at varius temperatures A Ali* & A K Nain Department f Chemistry, Jamia Millia Islamia, New Delhi 1\0025 Received 6 January 1996; revised$

1 Indian Jurnal f Chemistry Vl. 35A, September 1996, pp Thermdynamic study f frmamide + ethanl binary mixtures at varius temperatures A Ali* & A K Nain Department f Chemistry, Jamia Millia Islamia, New Delhi 1\0025 Received 6 January 1996; revised 22 March 199fj Densities, p, and viscsities, TJ, f pure frmamide (FA), ethanl and f their nine binary mixtures have been measured as a functin f cncentratin and temperature. The abve prperties have been fitted by empirical equatins stating their dependence n temperature and cmpsitin f the mixtures. The excess vlume, VE, excess viscsity, TJE and excess free energy f activatin f viscus flw, G >IE, and interactin parameter, d, have been calculated frm the experimental data and are studied as functin f cncentratin and temperature. All the excess functins are fund t be negative ver the entire range f cncentratin and temperature, except G >IE, which shws a typical behaviur. These prperties are discussed in terms f the nature f the mlecular interactins between cmpnent mlecules. Furthermre, the activatin enthalpies, AH *, and entrpies, AS *, f viscus flw are evaluated and their variatin with cncentratin has been discussed. Studies f excess thermdynamic functins such as excess vlume, excess viscsity, and excess free energy f activatin f viscus flw are useful in understanding the nature f intermlecular interactins in binary liquid mixtures 1-4. An attempt has been made t study the behaviur f frmamide (FA) + ethanl binary mixtures cvering the whle mle fractin range. FA has been chsen fr the present study since it serves as a cnvenient mdel system fr the investigatin f peptide and prtein slvent interactins. FA is unusual in its prperties, in that, it is strngly self-assciated thrugh extensive netwrks f hydrgen bnds-" and its dielectric cnstant and diple mment (e= and u= 3.68 D at K)? are very high. Ethanl mlecule, n the ther hand, has relatively lw value f dielectric cnstant and diple mment (e=24.55 and p.=1.69 D at K)1; yet self assciated thrugh hydrgen bnding>. Therefre, FA+ ethanl. will be an interesting binary slvent system fr the study f intermlecular interactins. In this paper, we reprt densities and viscsities f the binary mixtures f FA with ethanl at , , , and K, cvering the whle miscibility range expressed in terms f the mle fractin x f FA. Frm these experimental data, excess mlar vlume, excess viscsity, excess free energy f activatin f viscus flw, interactin parameter, enthalpy and entrpy f activatin f viscus flw are calculated. The significance f these parameters has been emphasised in understanding the intermlecular interactins between FA and Ethanl mlecules. Materials and Methds Frmamide was the same as in ur previus study", Ethanl (Merck, Germany) was further purified as described in the literature and was stred in a dry atmsphere. Density measurements were made using pycnmeter f bulb capacity 8 x 10-6m3 with graduated stem f 5.0 x 10-8 m' divisins. The marks n the stem were calibrated by making use f the knwn densities f triply distilled water. The viscsities were determined using Cannn-Ubbelhde viscmeter. The temperature f the test liquids and their mixtures was maintained t an accuracy f± 0.05 K in a thermstatic water bath. The experimental values f the density and viscsity f frmamide were kg m- 3 and x 10-3 kg m-is-i at K (literature values+? kg m? and 3.292xlO- 3 kg m-is-i/3.351 x 10-3 kg m-is-i), respectively. The clse agreement between experimental density and viscsity with thse reprted in the literature is an indicatin f the reliability f the present results. Results and Discussin The experimental values f density and viscsity f pure liquids and their binary mixtures as a

$752 INDIAN J CHEM, SEe. A, SEPTEMBER 1996 functin f mle fractin f FA and temperature are listed in Table 1. The dependence f P n temperature was checked by the plynmial Eq.$

2 752 INDIAN J CHEM, SEe. A, SEPTEMBER 1996 functin f mle fractin f FA and temperature are listed in Table 1. The dependence f P n temperature was checked by the plynmial Eq. (1), p(t)= 4 I Pi t i, tic,-0... (1) fr each binary slvent mixture. The Pi cefficients evaluated by means f least-squares methd are listed in Table 2 alng with the standard deviatins (p) fr each cmpsitin. The gdness f this fit equatin is ascertained by an average uncertainty f ± g cm- 3. The dependence f P n the cmpsitin f the binary mixtures was established by the plynmial Eq. (2), 11p(x)= I(1lpJ Xi,-0... (2) The 11Pi cefficients f Eq. (2) tgether with standard deviatins 0(1/ p) at each investigated temperature are given in Table 3. Equatin (2) is Table 2-Cefficients Table I-Densities (p) and viscsities (17) f FA+ethanul binary mixtures at varius temperatures x(fa) K p(kg m=') ': " " O.6I1RO I02l.7 IOl <) IJ II I3.1 17/( IU 'kg rn '~ ') ())UO(, 0.7(, J '>287 (1.1':" J I7 O.91'():" ,. 0:" (, iX21 1.2:" ':1045 I.A9A3 1.5.''>.' 1."Ol :l0 l.r,<)()(, 1.53'> '> 1.r,78'> (, A A ,, f Eq. I and standard deviatins a(p) f FA+ ethanl binary mixtures at varius temperatures x{fa), P, x I()2 P: x 10 P,X 10" P. x 10' f1(p)xiw II 98-3.AI9A ()0 O.532A A I.A

ALl et al.: TIffiRMODYNAMIC STIJDY OF BINARY MIXTURES OF FORMAMIDE WITH ETIIANOL. 753 fund t reprduce the experimental density well within ± 0.000286 g ern- 3.

3 ALl et al.: TIffiRMODYNAMIC STIJDY OF BINARY MIXTURES OF FORMAMIDE WITH ETIIANOL. 753 fund t reprduce the experimental density well within ± g ern- 3. The dependence f 1] n temperature fr the binary mixture under study was established thrugh the plynmial Eq. (3), 4 In 1]= Iln n, r, TIK i=-o... (3) The cefficients In 1]i alng with the standard deviatins a(ln 1]) fr each cmpsitin are listed in Table 4. Equatin (3) prduces the experimental values with an average uncertainty f ±2.91 x 10-6 kg m-1s- l Recently, Tassi et all' have als emphasized the data fitting fr binary systems using similar plynmials. The variatin f viscsity f FA + ethanl mixtures with mle fractin f FA (Table 1) des nt shw distinct maxima r minima such as thse assciated with N,N-dimethylfrmamide + ethanl" r water + ethanl'? binary mixtures. T(K) Table 4-Ceftlcients Table 3-1/ Pi cefficients f Eq. 2 fr FA+ ethanl binary mixtures at varius temperatures p,,1 PilxlO PilXlOJ p.,lxlo z P4-lxlOz a(p-i)xi : In I'/i f Eq. 3 and standard deviatin a(ln 1'/) f FA+ ethanl binary mixtures at varius temperatures x(fa) In 1'/" In 1'/1 x 10.1 In 1'/2 X 10' In 1'/3 x 10 7 In 1'/. x 10 1 " a(ln 1'/) x R ' ]] ? - Un D D DI ' '2-2.S J JO J9-2.J40J I A S.DI5-2.8J JJ Table 5-Cefficients A, f Eq. 5 and standard deviatins a(y~) fr FA + ethanl binary mixtures at varius temperatures T(K) AI A, A, A. A, a(y~) V~ (10-1>m'ml I) ' O.J425.u O.J034 O.OI4J ]] (U :I"i (U u 171-( 10-l kg m -I s- ') 29R.15 - I.J O.145J (l.oo31 J03.IS O.52SJ O.259S -0.52JI ]] I G.~ (kj ml- ') ]]

4 754 INDIAN J CHEM, SEC. A. SEPTEMBER 1996 The excess mlar vlume, V E, excess viscsity, YJ E and excess free energy f activatin f viscus flw, G~, have been calculated with the help f the fllwing relatins: VE= V-[(1-x)V I +xv 2 1 YJE= YJ - [( 1-x) YJ I + x YJ 21 G ~ = RI1ln YJ V- (1 - x)ln YJI VI - xln YJ2 V21.. (4).. (5).. (6) The mlar vlumes f binary mixtures were calculated using Eq. (7), V=[(1-x)M, +xm 2 ]!p.. (7) where suffixies 1 and 2 stand fr ethanl and FA; M, and M 2 are the mlecular weight f ethanl and FA, respectively; R is the gas cnstant and T is the abslute temperature. The variatins in VE, YJE and G*E with mle fractin f FA are shwn graphically in Figs 1-3. The excess functins were fitted with Eq. (8), 5 ye=x(.1-x) I A;(1-2x)i-'... (8) 1= 1 where ye is VE r YJE r G >It. The values f the cefficients Ai f these fitting equatins, tgether with the standard deviatins a(ye) calculated as,... (9) where m is the ttal number f data pints and n is the number f cefficients A; cnsidered (n = 5 in the present calculatin), have been listed in Table 5. The excess vlumes f mixing are negative ver the entire range f mle fractin, x, and temperature (Fig. 1). Such trends in V E have als been bserved fr benzyl alchl + isamyl alchl, isprpyl alchl" and N,N-dimethylacetamide + ethanl' binary mixtures. Mixing f FA with ethanl will induce the mutual dissciatin f the cmpnent mlecules 1.1 and the frmatin f hydrgen bnds between unlike mlecules. The frmer effect cntributes t an expansin while the latter effect is respnsible fr decrease in vlume. The bserved negative values f VE ver the whle range f cmpsitin f FA + ethanl mixtures shw that the main cntributin t V E is the decrease in the vlume due t hydrgen bnd frmatin between unlike mlecules. Mrever, the negative values f V E may als be, partly, due t the specific acid-base interactin between ethanl and FA mlecules by cnsidering ethanl as Lewis acid and FA as Lewis base. Very recently, H- Nam Tran'" emphasized the imprtance f acidbase interactins between tert-butylalchl and N,N-dimethylfrmamide/N, N-dimethylacetamide in rder t evaluate the interactin energy between alchl-amide systems. There may be anther surce f negative cntributin t VE due t the differences in the size and shape f the cmpnent mlecules in the mixture. The mlar vlumes f FA and ethanl at K are 3.99 x 10-5 and 5.86 x 10-5 m 3 ml- l, respectively, which might allw the cmpnent mlecules t fit int each ther's structure'", thereby, reducing the vlume f the mixture. The values f VE (Fig. 1) becme mre negative as the temperature f the system increases. The decrease f VE with the increase in temperature is explained by cnsidering the difference in the mlar vlumes f the tw liquids at different temperatures. The difference in the mlar vlumes f ethanl and FA is 1.95 x 10-5 m 3 at K while its value at K is 2.03 X 10-5 m''. This means that as the temperature f the mixture increases, the difference in the mlar vlumes f the tw liquids als increases, hence, the smaller mlecules f FA easily fit int the vids created by larger mlecules f ethanl- resulting in less increase in the vlume f the mixture, V. On the ther hand, the increase.... E -0.2 (\') E \ l '0.. UJ. 04 > ~--~----~----~----~--~ x, FA Fig. I-Excess vlume VE as a functin f mle fractin f FA and temperature; (0) , (e) ,,(0) , (ll.) and (&) K

ALl et al.: THERMODYNAMIC STIJDY OF BINARY MIXTURES OF FORMAMIDE WITH ETHANOL 755 in the temperature results an appreciable increase in the mlar vlume f ethanl, VI (5.86 x 10-5 m' ml- 1 at 298.

5 ALl et al.: THERMODYNAMIC STIJDY OF BINARY MIXTURES OF FORMAMIDE WITH ETHANOL 755 in the temperature results an appreciable increase in the mlar vlume f ethanl, VI (5.86 x 10-5 m' ml- 1 at K and 5.99 x 10-5 m" ml- l at K) and FA, V 2 (3.99 x 10-5 m 3 ml-l at K and 4.05 x 10-5 m 3 ml- l at K) due t the breaking f hydrgen bnds in the tw liquids. As a result, there willbe a decrease f VE, Eq. (4), with the increase in temperature f the mixture because the cmbined increase in VI and V 2 dminates ver V. Further, if the heat energy is supplied t the system FA + ethanl, the hydrgen bnds are brken and with the increase in the temperature increasingly large number f FA and ethanl mlecules will be invlved in the interactin, pssibly diple-diple+-acid-base'" interactins, with each ther; whereas in the case f pure liquids nly the frmer interactins are expected. Therefre, the value f VE which is resultant f these interactins becmes mre negative as the temperature f the system increases. Similar trends in d VE / dt have als been reprted fr benzyl + isamyl, + isprpyl alchl':'. The excess viscsity, 'IE, values are negative ver the entire range f mle fractin (Fig. 2), indicating that the dispersin frces are dminant, particularly, fr the systems having different mlecular size as in ur case. It is wrth t mentin that the values f the ml fractin, where minimum in 'IE and V E are bserved, are x and , respectively. These results indicate that the cmplex frmatin!", thrugh hydrgen bnd (- C = 0 HO -), between xygen atm f FA and ethanl takes place in the rati 1:1. The variatin f excess free energy f activatin f viscus flw, G *E, with mle fractin f FA \. "i"e,. -0.' '" -0 2 '" ':;! UJ~ ~ L-_.L.-_~_-'-_-<-_--' X. FA Fig. 2-Excess viscsity TIE as a functin f ml fractin f FA and temperature. The symbls are the same as in Fig. 1 t, E...,.. 1&.1- l!) x, FA Fig. 3-Excess free energy f activatin f viscus flw G *E as a functin f mle fractin f FA and remperature. The symbls are the same as in Fig. 1 and temperature (Fig. 3) seems t be typical. The values f G *E decrease sharply up t mle fractin x and then there is a steep rise in the value f G *E with maximum at abut x A decrease in G *E is again bserved which passes thrugh a less prnunced minimum at abut x befre reaching the value f pure FA. It has been marked that the psitins f minimum and maximum fr each curve (Fig. 3) differ slightly frm ne anther. This may be due t nn-systematic variatin f G *E with temperature. We, therefre, cnclude that the prcess f free energy change in the system under investigatin seems t prceed, mainly thrugh a fur step mechanism. The decrease in G *E in the first step may be attributed t the cmplex frmatin between unlike mlecules, which starts dissciating, due t specific interactin 13. as the free energy in the secnd step is increased. The decrease in G *E, n ging frm x t 0.85, may be due t predminant self-assciatin f the cmpnent mlecules, and finally, a small increase in G *E values may be assigned t the partial breaking f hydrgen bnds between ethanl mlecules as the cmpsitin f the mixture appraches t that f pure FA. A similar behaviur f G *E with cmpsitin and temperature has been reprted earlier fr benzyl alchl + isprpyl alchl 13 and methyl benzene + carbn tetrachlride" binary mixtures. The interactin parameter, d, a measure f strength f interactin between the cmpnent mlecules f the mixture, is anther useful parameter cnsidered here. At cnstant temperature,

$1404-0.3859-0.3413-0.2955-0.3117-0.3351 0.2688-0.2301-0.1584-0.1447-0.1565-0.1805 0.3865-0.1437-0.0868-0.0865-0.0959-0.1258 0.4950-0.0571-0.0444-0.0529-0.0674-0.\035 0.5952-0.0245-0.0026-0.0428-0.$

6 756 INDIAN J CHEM, SEC. A, SEPTEMBER 1996 Table 6-Grunberg-Nissan interactin parameter (d) f FA+ ethanl binary mixtures at varius temperatures x(fa) K \ \ Table 7-Enthalpies (IlH', entrpies (IlS *) and linear crrelatin factr (f), f viscus flw fr FA+ ethanl binary mixtures frm t K x (FA) IlH* (kjml- ' ) IlS* (J ml-'k- ' ) f Grunberg and Nissan'? prpsed the relatin' (Eq. 10), In 1]=(1- x) In 1]1+ xin 1]2+(1- x)xd... (10) where 1]is the viscsity f the mixture; 1]I and 1]2 are the viscsities f the tw pure cmpnents. The calculated values f d as a functin f mle fractin f FA and temperature are presented in Table 6. It is interesting t nte that d values exhibit maximum at abut x ; further cnfirming the frmatin f 1:1 ethanl-fa cmplexes as a result f strng interactin between the cmpnent mlecules". Finally, it is interesting t study the activatin parameters f viscus flw f FA + ethanl system. The enthalpy, ti H and entrpy, ti S f activatin f viscus flw were btained frm the fllwing equatirr'{'. RIn (1]V)=fR In (hn)- tis *J+ tih IT... (11) where V is the mlar vlume f the mixture, h is the Plank's cnstant, N is the Avgadr's number, and R is the gas cnstant. The plts f RIn (1]V) versus 1I T fr each binary mixture were fund t be linear indicating that ti H values are cnstant in the temperature range t K. The values f tih and tis btained frm the slpe and intercept f the abve plts alng with the crrelatin factr, f f Eq. (11) are given in Table 7. The values f llh* and lls* are all psitive and increase with an increase in the mle fractin f FA. It has been suggested earlier!' that the enthalpy f activatin f viscus flw may be regarded as a measure f the degree f cperatin between the species taking part in viscus' flw. In a highly structured liquid, there will be cnsiderable degree f rder and, hence, fr cperative mvement f entities, a large heat f activatin with relatively high value f entrpy f activatin is needed fr the flw prcess. Therefre, a perusal f Table 7 indicates that the frmatin f the activated species necessary fr viscus flw seems t be easy in the ethanl rich regin, wing t the lw value f llh, and becmes difficult as the mle fractin f FA in the mixture increases. When FA is added, there is instantaneus breaking f hydrgen bnds in ethanl mlecules, rendering the individual entities mre disrdered and, hence, less degree f cperatin. As a result, the net mlecular rder in the system under study is decreased, yielding high values f IIS *. This is in accrdance with the results reprted fr 1,2-ethanedil + N,N-dimethylfrmamide ll binary mixtures. Acknwledgement One f the authrs (AA) is grateful t the UGC, New Delhi fr financial supprt. References 1 Jshi S S, Aminabhavi T M & Balundgi R H, J chem eng Data, 35 (1990) 185.

ALl et al.: TIIERMODYNAMIC STIJDY OF BINARY MIXTURES OF FORMAMIDE WITH ETHANOL 757 2 Subbarangaih K, Murthy N M & Subrahmanyam S V, Acustica; 58 (1985) 105.

7 ALl et al.: TIIERMODYNAMIC STIJDY OF BINARY MIXTURES OF FORMAMIDE WITH ETHANOL Subbarangaih K, Murthy N M & Subrahmanyam S V, Acustica; 58 (1985) Pikkarainen L, Jchem eng Data, 28 (1983) Ali A & Nain A K, Thermchim Acta, in press. 5 Rhdewald P & Mldner M, J phys Chern, 77 (1973) Marcus Y, Intrductin t liquid state chemistry (Wiley- Interscience, New Yrk) Dean 1A. Lang's handbk f chemistry (McGraw-Hill, New Yrk) Ali A & Nain A K, Jchem Research(S), (1994) Stkes R H & Mills R, Viscsities f electrlytes and related prperties {Pergamn, New Yrk) 1965, p Osinska S T, PiekarskaA & Kacperska A, J sln Chern, 12 (1983) Crradini F, Marcheselli L, Marchetti A, Tagliazucchi M, Tassi L & Tsi G, Bull chem Sc Japan, 65 (1992) GeddesJ A,J Am chem Sc, 55 (1933) Islam M R & Quadri S K, Thermchim Acta, 115 (1987) Nam-Tram H. Jphys Chern, 98 (~994) Frt R J & Mre W R, Trans Faraday Sc, 61 (1965) 2102; 62 (1966) Slim H N, Riggi D I, Davli F & Katz M, Can J Chern, 53 (1975) Assarssn P & Eirich F R, Jphys Chem, 72 (1968) Jain D V S & Yadav 0 P, Indian J Chern, l2a (1974) Grunberg L & Nissan A H, Nature, 164 (1949) 799.

Thermodynamics and Equilibrium

Thermodynamics and Equilibrium Thermdynamics and Equilibrium Thermdynamics Thermdynamics is the study f the relatinship between heat and ther frms f energy in a chemical r physical prcess. We intrduced the thermdynamic prperty f enthalpy,