Heats of Solution and Mixing

Calculate the theoretical flame temperature when hydrogen burns with 400% excess dry air at 1 atm. The reactants enter at 100°C. 

Would burning a fuel with oxygen or with air yield a hi er adiabatic flame temperature  

Two workers were killed and 45 others hurt when a blast at the  

8 HEATS OF SOLUTION AND MIXING 4.8-1 Enthalpy Changes for Mixtures 

Your objectives in studying this section are to be able to  

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In a process for preparation of 2-methoxy-5-nitroaniline the anisidine salt was added to stirred sulfuric acid. An accidental deficiency of the latter prevented proper mixing and dissipation of the heat of solution, and local decomposition spread through the entire content of the 2000 1 vessel, attaining red heat. 

Chemical thermodynamics was developed by Pierre Maurice Martin Duhem (Paris, lo June i86i-Cabrespine, 14 September 1916), professor of theoretical physics in Bordeaux, who published on the equations for heats of solution and dilution which had been deduced by Kirchhoff, on the liquefaction of gaseous mixtures, eutectic and transition points for binary mixtures which can form mixed crystals, and a long series of papers on false equilibrium of doubtful value. He published some books on thermodynamics and later on the history of science. An important general thermodynamic equation (Gibbs-Duhem equation) was deduced independently by Gibbs and Duhem. ... 

Enthalpy-concentration data. An enthalpy-concentration diagram for a binary vapor-liquid mixture of A and B takes into account latent heats, heats of solution or mixing, and sensible heats of the components of the mixture. The following data are needed to construct such a diagram at a constant pressure (1) heat capacity of the liquid as a function of temperature, composition, and pressure (2) heat of solution as a function of temperature and composition (3) latent heats of vaporization as a function of composition and pressure or temperature and (4) boiling point as a function of pressure, composition, and temperature. 

Specific heat heat of solution or mixing. Heat of vaporization and fusion. 

Lundin (1966) measured heat of solution and calculated the heat of mixing for alloys in the La-Gd system. A plot of the heat of mixing versus composition for a binary system should show abrupt inflections at major phase boundaries. Lundin used a liquid-metal-soludon calorimeter that employed a liquid indium bath. The calorimeter was calibrated using solid indium sanq>les and to avoid alloying between the rare earth metals and the molten indium, the indium bath was changed after... 

DeBoer et al. (1980) presented calculated values for the enthalpy of formation, the limiting partial heats of solution and the heat of mixing of several binary alloys based on scandimn. The authors pointed out that the scarcity of experimental information on the heat of alloying of scandium alloys makes the comparison of the... 

Equation (21) is of enormous practical value. The knowledge of the chemical potential of a solute X in almost arbitrary solvents allows for the calculation of almost any equilibrium of solutes between different solvents and between solvents and vapors. Thus it allows for the calculation of vapor pressures, partial pressures of components over mixed fluids, and partition coefficients of all kinds. A few examples are given below. Beyond the calculation of free energies and hence of chemical potentials equation (20) also is the key to the calculation of heats of solution, and even of surface tensions. For the sake of brevity we do without details here. 

For CaCl2-NaCl solutions, various physical properties have also been determined. The solutions density (Table 2.31), and the activity coefficients of the ions at temperatures to 250°C and 400 bars (395 psi) pressure have been determined by Oakes (1992), and the heat of dilution and mixing from 100 to 300°C and 21.5 MPa (145 psi) pressure by Oakes et al (1998). Low temperature Raman spectroscopic investigations have been made by Samson and Walker... 

Iodoform reaction. To 0 5 ml. of acetone add 3 ml. of 10% KI solution and 10 ml. of freshly prepared sodium hypochlorite solution and mix well. A pale yellow precipitate of iodofonn is rapidly formed without heating. Acetophenone similarly gives iodoform, but the mixture must be shaken vigorously on account of the limited solubility of acetophenone in water. Benzophenone does not give iodoform. 

Undersaturated The same quantities of solute and solvent are mixed, as for the above ease, but the system is then heated for about 20 min above the required temperature (if solubility inereases with temperature) so that most, but not all, of the solid is dissolved. The solution is then eooled and agitated at a given temperature for a long period, to allow the exeess solid to deposit and an apparent equilibrium to be reaehed. 

To prepare the aqueous phase, one should begin by taking one-third of the water and heating it to 90°C. With good mixing at 120 rpm, slowly introduce the methocel into the hot water. Once the methocel is well dispersed, add the remaining two-thirds of cold water and cool the mixture to 25°C. Mix at 25°C until the solution becomes dear. Add the NH4OH to the solution and mix for at least 30 min. Heat the water phase to 40°C and apply a vacuum for at least 30 min. 

The ethyl acetate solution is then washed with water, dried and evaporated. To remove any selenium still present, the residue is dissolved in 200 cc of methanol and mixed with 100 g of iron powder and 2 g of active carbon. The mixture is heated for 30 minutes with stirring under reflux, then filtered with suction, washed with methanol and the solution evaporated in vacuo. The residue is then chromatographed on 900 g of aluminum oxide. The residues of the evaporated benzene and ether fractions are treated with active carbon in methanol or acetone, evaporated again, and the residue recrystallized from a mixture of acetone and ether. There are obtained 17.5 g of pure 1-dehydro-17a-methyl-testosterone which melts at 163° to 164°C. 

Heats of solution are the basis for instant cold packs and instant hot packs used for the first-aid treatment of minor sprains and pulled muscles. These packs have two separate compartments. One contains water, and the other contains a salt NH4 NO3 for cold packs and MgSO. or CaCl2 for hot packs. Kneading the pack breaks the wall between the compartments, allowing the salt to mix with water. As the salt dissolves to form an aqueous solution, the temperature of the pack changes. Heat is absorbed or released only as the salt dissolves, however, so after all of the salt has dissolved, the pack gradually returns to room temperature. Further manipulation of the pack has no effect. 

For mixtures of liquids and for solutions, the heat of mixing (heat of solution) may be significant, and so must be included when calculating the enthalpy of the mixture. 

Heats of mixing and heats of solution are determined experimentally and are available in the handbooks for the more commonly used solutions. 

Restoring the solution concentration by adding dry solute or mixing with concentrated solution can save energy costs as it avoids heat of evaporation and the need for expensive plants. The method can be suggested successfully for small-scale production, at a low-technological level process, where the initial solution mass is small. Indeed, the main hurdle of this technique is the increase of the solution mass, even if a constant loss in volume of syrup (9-14%) is due to adherence to the food pieces (Bolin et al., 1983). 

Water-miscible solvents alone can be used when the drug is chemically unstable in the presence of any water. The number of solvents available for this purpose is extremely limited. The classic review of this subject was made in 1963 (Spiegel and Noseworthy), and some 30 years later, no additional solvents are available. This is unlikely to change in the near future due to the extensive effort necessary to determine the safety of a solvent used as a vehicle. When a nonaqueous vehicle is used, one can invariably expect some degree of pain upon injection, and subsequent tissue destruction is possible. This damage may be due to the heat of solution as vehicle mixes with body fluids it may be associated with tissues rejecting the solvent or, it may be an inherent property of the solvent. 

This question pertains to substances that will chemically react with water, particularly at normal ambient conditions. Some concentrated acids and bases can generate considerable heat of solution or heat of dilution when mixed with water. However, this can be considered a physical effect rather than a chemical reaction. 

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