Entropy of dissolution

The above conclusion is unfortunate for the case of polymeric solutes, because then-entropies of dissolution are unusually small. The repeat units can not become as disordered as can the corresponding monomer molecules since they are constrained to be part of a chain-like structure. Such disordering is particularly difficult if the chain is stiff. Thus, in this situation dissolution is even less likely. Crystalline polymers are also more difficult to dissolve than are their amorphous counterparts since the enthalpy of dissolution also contains a large, positive contribution from the latent heat of fusion. 

As discussed in Section V.3.2.2.2, the entropy of nickel hydroxide was calori-metrically measured with sufficient accuracy [69SOR/KOS], [78ENO/TSU] that, in fact, the value of the entropy of dissolution contributes to the knowledge of the partial molar entropy S (Ni ), see Equation (V.45). 

One can see from this that a general equation for the configurational entropy or entropy of dissolution involved in forming a solution is... 

Let s continue one step further with this example and calculate the total entropy of dissolution... 

What we have just done suggests a new and more general form of equation (15.6) for configurational entropy or entropy of dissolution in multi-site, multi-component crystalline solutions, which is... 

When a nonpolar molecule is surrounded by water, stronger than normal water-water interactions are formed around the solute molecule to compensate for the weaker interactions between solute and water. This results in an increasingly ordered arrangement of water molecules around the solute and thus a negative entropy of dissolution. The decrease in entropy is roughly proportional to the nonpolar surface area of the molecule. The association of two such nonpolar molecules in water reduces the total nonpolar surface area exposed to the solvent, thus reducing the amount of structured water, and therefore providing a favourable entropy of association. 

The solubilities of the scale-forming salts barium and strontium sulphates in aqueous solutions of sodium chloride have been reviewed by Raju and Atkinson (1988, 1989). Equations were proposed for the prediction of specific heat capacity, enthalpy and entropy of dissolution, etc., for all the species in the solubility equilibrium, and the major thermodynamic quantities and equilibrium constraints expressed as a function of temperature. Activity coefficients were calculated for given temperatures and NaCl concentrations and a computer program was used to predict the solubility of BaS04 up to 300 °C and SrS04 up to 125 °C. 

Values of the differential entropy of dissolution of lyomesophases in isotropic liquids are very small. For instance, in the dimethyldecylphosphine oxide... 

Both entropy and enthalpy change have to be considered when dissolving a salt in any solvent Dissolution can lead to either a positive or negative overall entropy change. In polymer electrolytes, a negative entropy of dissolution is common and can be an important consideration at higher temperatures. This effect arises because the dielectric constant of the solvent polymer (solid or liquid) is usually... 

The standard molar entropy of dissolution, Asoi S° pertains to the transfer from a 1 atm gas state to a 1 mol L solution and hence includes compression of the gas phase from 1 mol contained in 24.61 L (at 300 K) to 1 mol present in 1 L. Since theoretical calculations disregard volume contributions, it is proper to exclude the entropy of compression equal to -R In 24.61 = -26.63 J K" mol, and instead to deal with Thus,... 

The entropy of dissolution of H2 gas into a(Fe,Al) alloy at 600°C, evaluated from the hydrogen solubility measurements [1957Lie, 1957Wit] varies from -160 J-K per mole of H2 for pine aFe to -140 J K" per... 

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