Thermodynamic study of (heptane+amine) mixtures. III: Excess and partial molar volumes in mixtures with secondary, tertiary, and cyclic amines at 298.15K

Thermodynamic study of heptane+secondary, tertiary and cyclic amines mixtures. Part IV. Excess and solvation enthalpies at 298.15K

“…As a general observation, the main result that H E andH j are positive in the whole mole fraction range for all mixtures examined can be qualitatively explained with a net destruction, during the mixing process, of the structural order present in the neat liquids (H-bonding and dipole-induced dipole interactions in amines), in agreement with the interpretative scheme proposed by Patterson [19], and confirmed by the positive V E [2,3,20], G E [21] and H E [1,21] for n-alkane + alkylamine mixtures. Moreover, all amine categories show H E and H • j (j = 1,2) (except H • 2 of cy-heptylamine) that decrease as the amine size increases, exhibiting nicely parallel trends.…”

“…This latter is composed of one Lund Syringe Pump Mod. 6120 and two General Control pumps which operate on a number of Hamilton gas-tight syringes of capacity ranging from 100.0 to 1000 L. With this system we are able to make accurate injections starting from a minimum of 1 L, with precision 0.5%, and to measure accurate heat effects as small as 0.01 J, with sensitivity 0.5 W. To convert the volume injected into mass, we used density values for all substances by us measured [3]. The uncertainty in the mixture composition, almost determined by the precision of the syringe, leads to an analogous uncertainty in the mole fraction of the final mixture.…”

“…The magnitude of solv H • , and its variation with molecular structure, mostly depend on vap H • , as H • contributes less than 25% to solv H • . Consequently, the accuracy of this quantity is practically the same as that of vap H • , which is usually better than 0.5% and does not exceed 0.2 kJ mol −1 [4]. Since the interaction between a solute and the surrounding solvent molecules takes place through surface contact, we have taken the van der Waals surface area S w [22] as molecular parameter for comparison among different substances.…”

“…To fill this gap, in previous papers in this series, we reported and discussed H E [1] and V E [2] of heptane + primary amines, and V E [3] of heptane + secondary and tertiary n-alkyl, primary cycloalkyl, heterocyclic secondary amines. As a continuation, for the same mixtures of Ref.…”

“…As a continuation, for the same mixtures of Ref. [3] and using the same calorimetric technique as in Ref. [1], we have measured the partial molar enthalpy of each component in the whole mole fraction range, and from that we have obtained the excess enthalpy in the entire mole fraction range and the infinite dilution partial molar enthalpy, H • of each component.…”