Heat capacity aqueous systems

D ans, J. Surawski, H. Synowietz, C. Schafer, K., Ed., Part IV "Densities of Liquid Systems and Their Heat Capacities. Part B. Densities of Binary Aqueous Systems... 

However, two types of systems are sufficienfry important that we can use them almost exclusively (1) liquid aqueous solutions and (2) ideal gas mixtures at atmospheric pressure, hr aqueous solutions we assume that the density is 1 gtcvc , the specific heat is 1 cal/g K, and at any solute concentration, pressure, or temperature there are -55 moles/hter of water, hr gases at one atmosphere and near room temperature we assume that the heat capacity per mole is R, the density is 1/22.4 moles/hter, and aU components obey the ideal gas equation of state. Organic hquid solutions have constant properties within 20%, and nonideal gas solutions seldom have deviations larger than these. 

Medium-chain alcohols such as 2-butoxyethanol (BE) exist as microaggregates in water which in many respects resemble micellar systems. Mixed micelles can be formed between such alcohols and surfactants. The thermodynamics of the system BE-sodlum decanoate (Na-Dec)-water was studied through direct measurements of volumes (flow denslmetry), enthalpies and heat capacities (flow microcalorimetry). Data are reported as transfer functions. The observed trends are analyzed with a recently published chemical equilibrium model (J. Solution Chem. 13,1,1984). By adjusting the distribution constant and the thermodynamic property of the solute In the mixed micelle. It Is possible to fit nearly quantitatively the transfer of BE from water to aqueous NaDec. The model Is not as successful for the transfert of NaDec from water to aqueous BE at low BE concentrations Indicating self-association of NaDec Induced by BE. The model can be used to evaluate the thermodynamic properties of both components of the mixed micelle. 

Heat storage in biological systems is much the same as for the previous material classes. For example, the heat capacity of biological fluids, which are heterogeneous suspensions and mixtures, can be approximated by Eq. (4.47). In instances where the biological fluid or food substance is an aqueous-based suspension or solution of fat and solids, the specific heat (heat capacity per unit weight in J/g K) can be approximated as... 

Calculation of A//e -quantities from the dependence of AG on temperature is less reliable than direct calorimetric measurements (Franks and Reid, 1973 Frank, 1973 Reid et al., 1969). However, disagreement between published A//-functions for apolar solutes in aqueous solutions may also stem from practical problems associated with low solubilities (Gill et al., 1975). Calorimetric data have the advantage that, as theory shows, the standard partial molar enthalpy H3 for a solute in solution is equal to the partial molar enthalpy in the infinitely dilute solution, i.e. x3 - 0. A similar identity between X3 and X3 (x3 - 0) occurs for the volumes and heat capacities but not for the chemical potentials and entropies. The design of a flow system for the measurement of the heat capacity of solutions (Picker et al., 1971) has provided valuable information on aqueous solutions. 

In aqueous solution polymerization a water-soluble monomer is polymerized to a water-soluble polymer. For example, polyacryUc acid is produced on a large scale by free radical techniques in this manner [10]. Again, fhe non-flammabiUty and high heat capacity of water are advantageous. Such polymerizations in homogeneous solution can, in some cases, offer better molecular weight control by comparison to polymerization in a multiphase system. 

The thermodynamic functions that describe this equilibrium include the equilibrium constant, the enthalpy, the free energy, and the heat capacity. These are all predictable, and can be derived by a variety of routes, each route yielding the same values for the functions. The equation describing the reaction is sufficient to allow for the initiation of all appropriate calculations. In contrast, the rate of the reaction, and the temperature dependence of the rate of the reaction are inherently unpredictable, and require empirical measurement. In particular, the equation describing the reaction stoichiometry cannot, a priori, enable the kinetic equations to be predicted. Detailed knowledge of the reaction mechanism would be required. This distinction between the inherent predictability of equilibrium conditions, and the empirical nature of kinetic conditions, must be borne in mind when considering the phase behavior of aqueous systems. 

G3. Landolt-Bornstein. Densities of Binary Aqueous Systems and Heat Capacities of Liquid Systems, New Series, Group IV Springer-Verlag Berlin, 1977 Vol. lb. 

A single homogeneous phase such as an aqueous salt (say NaCl) solution has a large number of properties, such as temperature, density, NaCl molality, refractive index, heat capacity, absorption spectra, vapor pressure, conductivity, partial molar entropy of water, partial molar enthalpy of NaCl, ionization constant, osmotic coefficient, ionic strength, and so on. We know however that these properties are not all independent of one another. Most chemists know instinctively that a solution of NaCl in water will have all its properties fixed if temperature, pressure, and salt concentration are fixed. In other words, there are apparently three independent variables for this two-component system, or three variables which must be fixed before all variables are fixed. Furthermore, there seems to be no fundamental reason for singling out temperature, pressure, and salt concentration from the dozens of properties available, it s just more convenient any three would do. In saying this we have made the usual assumption that properties means intensive variables, or that the size of the system is irrelevant. If extensive variables are included, one extra variable is needed to fix all variables. This could be the system volume, or any other extensive parameter. 

---