T H E RRIC)DYSAR1IC STUDIES OF THE SYSTEM : ACETOSE-CHLOROFORJI. 11. THE RELATION OF EXCESS MIXING FUNCTIONS TO hSSOCI,-ITION COMPLEXES' B Y EDWARD R. IcESRIiS S t d i n q Chemistr?]Lahoratorij, Y a l e University,Xeic H a v m , Connecticut Kreerved ./lugus1 8 , 1960
The assumption of I : 1 and 1:2 association complexes in the acetone-chloroform system is sufficient for close reproduction of previously reported excess free energy of mixing data and Hirobe's calorimetric heat of mixing data throughout the experimental range of composition and from 25-50'. Equilibrium constants are obtained from a linear plot of the type used by McGlashan and Rastogi. The heat of association for the 1 :1 complex is in agreement with previous estimates for the . . O=C hydrogen bond. energy of the C:-H .
Introduction I n a previous paper,2 herein denoted (I), excess free energies of mixing, GxE, were reported for the acetoiie-chloroform system a t 25, 35 and 50". These data were fitted to a function of mole fraction similar to those used by W ~ h l and , ~ from the temperature-dependence of parameters, it proved possible to calculate the heats of mixing4 with fair precision, by fitting an equation to selected data points. Rock and S ~ h r o d ehave r ~ ~recently ~~ raised questions about the precision of the reported data, which led to a re-examination of the acetone-chloroform system to see how closely one could predict heat of mixing data from activity measurements. It mas found that the treatment of RiIcGlashan and Rastogi6could be applied to the acetone-chloroform system. Calculated values of HxE agreed with the experimental values of H i r ~ b ealmost ,~ to the precision of the original data. This evidence that the GxE data is consistent with HsE measurements serves to refute contentions'J of unreliability of measurements made with the same equilibrium still. Association Complexes.-McGlashaii and Itastogi6 have given a theoretical treatment for the case where two components, A and B, form complexes AB and AB,. I n this paper, every mention of a numbered equation refers to that given in the paper of McGlashan and R a ~ t o g i . ~Acetone ,~ and chloroform are designated as A and B, respectively. K , and Kz, the equilibrium constants for the formation of complexes AB and ABa, respectively, mere obtained by least squares fitting of the data, to the relation of equation 12. Standard deviations for the equilibrium constants a t each temperature were of the order of 0.016 to 0.027. Clearly. for the calculation of H x ~ knowledge , of the variation of the equilibrium constants with temperature is required. Since K's are known at (1) Based in part on the AIS Thesis of E d a a r d R. Kearns, Purdue Unirervity, August 2 , 1957. (2) C . R. XIuell
