Molar enthalpy of solution

First let us consider a solution process in which solute is transferred from a pure solute phase to a solution. The molar differential enthalpy of solution, A o H, is the rate of change of H with the advancement soi at constant T and p, where soi is the amount of 

Thermodynamics and Chemistry, second edition, version 3 2011 by Howard DeVoe. Latest version www.chem.umd.edu/themobook 

The value of Asoi f at a given T and p depends only on the solution molality and not on the amount of solution. 

When we write the solution reaction as B B(sln), the general relation AxX = 

The molar enthalpy of solution at infinite dilution, is the rate of change 

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Thalium, excess entropy and partial molar enthalpy of solutions of noble metals in, 133... 

Randall, M. 1. 264. 265 Raoult s law 268-73 and phase equilbria 419. 423 standard state 289 Rectilinear diameters, law of 393 Redlich-Kister equation 220, 362 Redlick-K wong equation 256 relative apparent molar enthalpy of solutions 356-7... 

When a solute is dissolved in a solvent, heat may either be evolved (as with sulfuric acid in water, where strong heating is observed) or absorbed (as with ammonium nitrate in water, where strong cooling is observed). Thus the dissolution may be either exothermic or endothermic, and the standard molar enthalpy of solution, is then either negative or positive. The sign of AsaJl°... 

The term (7/Sig2Si04,meit Mg2Si04,oiivine) is the molar enthalpy of solution of pure forsterite in a pure Mg2Si04 melt, and is equivalent to the molar enthalpy of fusion at r =... 

Solute retention as a function of temperature at constant pressure is seen to be dependent on the partial molar enthalpy of solute transfer between the mobile and stationary phases, the neat capacity of the supercritical fluid mobile phase and the volume expansivity of the fluid. The model was compared to chromatographic retention data for solutes in n-pentane and CO2 as the fluid mobile phase and was seen to fit the data well. 

For the calculation of the net adsorption enthalpies of transactinides on metal surfaces the partial molar enthalpies of solution and the enthalpy of displacement are required. These values can be obtained using the semi-empirical Miedema model [66-70] and the Volume-Vacancy or Surface-Vacancy model [32,70,71]. Data for these calculations are given in [34,72,73]. 

The slopes of these lines provide partial molar enthalpies of solution of 97.5 4.7 and 89.2 2.6 kJ mol1 for NaBr and Nal, respectively, where the thermodynamic reference state is the solid halide. The solvation enthalpies derived from these values are —265.6 9.9 and —225.0 7.9 kJ mol-1 for bromide and iodide ion, respectively. The salts are considered to dissolve in the metal as the dissociated ions, solvated by liquid metal, and the solutions show large deviations from ideal but small deviations from regular behaviour.16 The solubilities of potassium chloride in liquid potassium and in... 

In equations (40) and (41), Xg " is the mole fraction solubility of the solid solute at an absolute temperature T, a is the apparent molar enthalpy of solution, b is the apparent molar entropy of solution, and c and c" are constants. The combined equation, attributed to Valentiner, has been used by Grant et al. (1984) in the... 

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.

Figure A 16 Molar enthalpy of solution of NiS04-6H20(cr) at 25 C.325...

Calorimetric data for solutions are handled in a number of different ways, which can be confusing. In addition to integral and differential heats of solution and the partial molar enthalpy of solution, we also have the apparent partial molar enthalpy, the relative partial molar enthalpy, and the relative apparent partial molar enthalpy. To see how these terms cirise, consider the following. 

There is one thorough calorimetric study of the enthalpy of reaction of thorium with hydrogen, but at one temperature only, by Picard and Kleppa [1980P1C/KLE], who measured the partial molar enthalpy of solution (H2, 700 K), as a function of the... 

The selected value is that from the calorimetric study [1980P1C/KLE], since that has an exphcit integration of the partial molar enthalpy of solution across the whole region from H/Th = 0 to 2 and was carried out at the lowest temperature, where the effects of non-stoichiometiy are smallest. 

To answer this question we must first determine the molar enthalpies of solution and multiply this by the number of moles of solid dissolved to gel the actual amount of heat released. 

K, respectively. The partial molar enthalpies of solution at infinite dilution obtained from these results are collated in Table 44. The heat of... 

Table 44 Partial molar enthalpies of solution of Dy, Er, and Eu in tin at infinite dilution...

This is the same as eg. fi . 2i). That is, the empirical fit in eq. (1. 2 ) is of the form expected from the theoretical considerations und the assumption that the partial molar enthalpy of solute at infinite dilution is constant. In... 

The slope of the curve at sol=0 is Aso H°°, the molar enthalpy of solution at infinite dilution. If the measurements are made at the standard pressure, AsoiH° is the same as the standard molar enthalpy of solution, Asoi-H °, because the standard molar enthalpy of a solute is the molar enthalpy at p=p° and infinite dilution. 

From tabulated values of molar enthalpies of formation, we can calculate molar integral enthalpies of solution with Eq. 11.4.11 and molar integral enthalpies of dilution with Eq. 11.4.12. Conversely, calorimetric measurements of these molar integral enthalpies can be combined with the value of AfH(B ) to establish the values of molar enthalpies of solute formation in solutions of various molalities. 

The reference state for the solute is the solute at infinite dilution. To relate Lb to molar enthalpies of solution, we write the identity... 

We can find the standard molar enthalpy of solution of B from the temperature dependence of the solubility. Combining Eqs. 12.1.12 and 12.5.6, we obtain... 

At the standard pressure, Aso1,b7 ° is the same as the molar enthalpy of solution at infinite dilution, Aso[,bH°°. 

From five calorimetric runs, the average experimental value of the standard molar enthalpy of solution of gaseous HCl at 298.15K is Asoi,bF(° = —74.84 kJmol . ... 

The reaction can be assumed to go to completion, and the amount of KCl was in slight excess, so the amount of AgCl formed was equal to the initial amount of AgNOj. After correction for the enthalpies of diluting the solutes in the initial and final solutions to infinite dilution, the standard molar reaction enthalpy at 298.15 K was found to be Ar // ° = —43.042 kJ mol . The same workers used solution calorimetry to obtain the molar enthalpy of solution at infinite dilution of crystalline AgNOs at298.15K Asoi,b// = 22.727kJmor ... 

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