Dilution, enthalpy

Thermochemical and thermophysical properties are suitable for the elucidation of the structure-performance relationships of surfactants in solutions. The measurement of, for instance, integral dilution enthalpies provides an appropriate experimental basis [50,51]. The concentration functions of the dilution enthalpies of ammonium dodecane 1-sulfonate (Fig. 29) show a distinct depen-... 

A 7/°(C.2l I5OI 1 60112O, sin) is, therefore, the apparent molar enthalpy [25] of ethanol in a solution containing 60 mol of water. In other words, the value relies on identical enthalpy contents for the water molecules in solution and as a pure liquid. A dilution enthalpy, for example, from C2H5OH 60H2O to C2H50H 100H20, calculated as... 

This expression enhances the fact that the heat release rate is a function of the conversion, but also of the varying volume. The dilution of the reaction mass by the feed will contribute to slow the reaction. Usually with a constant feed rate and as long as the volume varies in the cylindrical part of the reactor, V(t) is a linear function of time. In addition to the pure heat of reaction, the mixing effect of the feed with the reaction mass can be accompanied by thermal effects, for example, dilution enthalpy or mixing enthalpy. 

The initial work at Bartlesville has concentrated on measurements of enthalpy changes from dilution and adsorption for surfactant systems. From the observed dilution enthalpy changes, critical micelle concentrations have been determined, and standard state enthalpies of micel lization have been calculated. In the studies on adsorption, several properties are of interest the enthalpy of adsorption, the amount of surfactant adsorbed, the surface area of the solid and determining whether the adsorption is reversible. The kinetics of adsorption and desorption are also of interest. 

Figure A-16 Molar enthalpy of solution of NiS04-6H20(cr) at 25°C. Experimental data from Goldberg et al. [66GOL/RID] o dotted curve calculated according to Equation (1X.44) in [97ALL/BAN] dash dotted curve calculated according to the chord method, see Equations (8 - 2 - 19) and (8 - 2 — 20) of Hamed and Owen [58HAR/OWE] solid ciuwe calculated vdth an adjustable Debye-Hilckel parameter, A, and a term linear in /, ((A.27), 298.15 K) derived from dilution enthalpies [56LAN/M1E] x mean value of Aj /7° ((A.27), 298.15 K), dash line.

The chemical potential gives the partial molar Gibbs energy of dilution. The partial molar dilution enthalpy and the partial molar dilution entropy are given by... 

Standard thermodynamic manipulations yield the infinite dilution enthalpy, entropy, and isobaric heat capacity of hydration (Plyasunov, O Connell, and Wood 2000 Sedlbauer, O Connell, and Wood 2000). For example. 

Infinite Dilution Enthalpies of Solution for Some Ionic Compounds ... 

The value of A//sat can differ from the infinite dilution enthalpy of solution AH defined in Section 7.6 for two reasons ... 

Fig. 4. The thermal cycle for getting dilute enthalpy from concentration Cz to Ci According to the thermal cycle, the corresponding computing equations are following...

Table 6. Dilute enthalpies A H(c) (kj. mol-i) for Cu in CUCI2+I mol.dm-3KCl electrolyte solution.

It is worth noting that, depending on the type of PE used, the electrostatic contribution for PEs are the dominating force and therefore it is possible to omit the Hory enthalpy term in this cases [23]. If the PE is very weak, the free enthalpy of dilution, AH, is only correctly obtained, when the electrostatic and Flory-Huggins polymer dilution enthalpy terms are added [49]. 

The original theoretical assumption that the low charge density has a negligible influence on the structure is supported by experimental measurements of Safronov et al. [49]. Their results showed no influence from salt concentration, and therefore of the charge density, on the dilution enthalpy or total energy of chitosan, (a weak PE) [49]. 

Simonin JP, Bernard O, Papaiconomou N, Runz W. (2008) Description of dilution enthalpies and heat capacities for aqueous solutions within the MSA-NRTL model with ion solvation. Fluid Phase Equilibr 264 211-219. 

The term A/y i,] accounts for the dilution enthalpy observed upon titration of lipid vesicles into the surfactant solution and can be detennined in a separate experiment by titrating lipid vesicles into water. When the reversed experiment is performed, i.e. the titration of a monomeric surfactant solution to a vesicles suspension in the cell, then equation (16) has to be differentiated with respect to D, and one obtains ... 

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