Mean molal heat capacities

Sometimes tabulated values of the mean molal heat capacities Cp (T) are more easily accessible than C (T data, with respect to a reference temperature of T = 25°C (see Table 2-45). Since Cp is defined over the range T and T, by... 

Mean Molal Heat Capacities of Gases Between 25°C and T°C (Reference pressure = 0)... 

In the event the mean molal heat capacity data are available with a reference temperature other than = 25°C (see Table 2-46 for data with = 0°C), the following equation can be used to calculate AH (Tj) ... 

An alternative representation is useful when data on mean molal heat capacities Cj (T) are available with 25 C as the reference temperature (T ). Then the equation... 

Method 3. Use mean molal heat capacity data from Table 2-46 with reference conditions of 0°C and 1 atm. Then the equation for T, is... 

The cost of refrigerant is 11.5 GJ 1, the mean molal heat capacity of the vapor is 40 kJ kmol-1K-1, and the latent heat of acetone is 29,100 kJ kmol-1. 

Once the standard potential of Cell I has been determined precisely, calculations of the mean activity coefficient, y , of HC1 and the primary and secondary medium effects using well-known relations are relatively simple tasks. Using empirical equations of the type E = a - - bT + cT2 and E° = a0 + b0T + c0T2, it is possible to calculate the molal enthalpies and heat capacities. These types of calculations are demonstrated in many... 

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. 

This table contains standard state thermodynamic properties of positive and negative ions in aqueous solution. It includes en-thcdpy and Gibbs energy of formation, entropy, and heat capacity, and thus serves as a companion to the preceding table, Standard Thermodynamic Properties of Chemical Substances . The standard state is the hypothetical ideal solution with molality m = 1 mol/kg (mean ionic molality in the case of a species which is assumed to dissociate at infinite dilution). Further details on conventions may be found in Reference 1. 

Partial molal entropy data in ethanol are nearly as sparse as the heat capacity data. The only comprehensive entropy data in this solvent are those of Jakuszewski and Taniewska-Osinska, who report 5 for HCl and several alkali metal halides in ethanol. Ionic entropies have been calculated for the alkali metals from free energies and enthalpies of solvation, but since extra-thermodynamic assumptions were necessary, the meaning of the values is questionable. Ionic entropies in ethanol are somewhat more negative than in methanol and considerably more negative than in water. 

The specific heat capacity of water is 4.18 J K g (see Table 7.1), so we have demonstrated by calculation that 1 molal NaCl(aq) has a lower specific heat capacity than water. This means that it is easier (less heat is required) to raise the temperature of 1 g of 1 molal NaCl(aq) by 1 K than to raise the temperature of 1 g of water by 1 K. Stated another way, a given quantity of heat will cause a greater temperature change in 1 g of 1 molal NaCl(aq) than in 1 g of water. In general, the specific heat capacity of a salt solution will always be lower than that of water. See Figure 14-7. The reason is that when an ion is... 

---