Heat of dissolution

The heat of dissolution is the amount of heat produced, or used, by the dissolution process of a compound. It can be exothermic or endothermic. For example, the dissolution of sodium hydroxide is exothermic. 

Calorimeters are devices that measure heat of reactions (enthalpy change). In the adjoining figure, a bomb calorimeter is shown. It is so called because the reaction occurs in a steel container at the center of the calorimeter, that is known as a bomb . The bomb is inserted in another container filled with water and isolated. The compound is then inserted in a bomb and ignited by electricity. The heat released by the combustion of the compound in the bomb warms up the water. In other words, the heat produced by the combustion of the compound is absorbed by the bomb and the water. For this reason. 

Heat of reaction = Heat absorbed by bomb + Heat absorbed by water 

After the reaction is completed, the temperature change is measured. Heat absorbed by the bomb or water is calculated with the following formula. 

Reaction ( bomb water) Reaction ( bomb water  

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The heat of dissolution of potassium permanganate in water varies between 41.84 kJ/mol (10.62 kcal/mol) in dilute solution to... 

Potassium siUcates are manufactured in a manner similar to sodium siUcates by the reaction of K CO and sand. However, crystalline products are not manufactured and the glass is suppHed as a flake. A 3.90 mole ratio potassium siUcate flake glass dissolves readily in water at ca 88°C without pressure by incremental addition of glass to water. The exothermic heat of dissolution causes the temperature of the solution to rise to the boiling point. Lithium sihcate solutions are usually prepared by dissolving siUca gel in a LiOH solution or mixing colloidal siUca with LiOH. 

The partial molar entropy of a component may be measured from the temperature dependence of the activity at constant composition the partial molar enthalpy is then determined as a difference between the partial molar Gibbs free energy and the product of temperature and partial molar entropy. As a consequence, entropy and enthalpy data derived from equilibrium measurements generally have much larger errors than do the data for the free energy. Calorimetric techniques should be used whenever possible to measure the enthalpy of solution. Such techniques are relatively easy for liquid metallic solutions, but decidedly difficult for solid solutions. The most accurate data on solid metallic solutions have been obtained by the indirect method of measuring the heats of dissolution of both the alloy and the mechanical mixture of the components into a liquid metal solvent.05... 

TABLE 7.1 Heats of Breakup First Heats of Dissolution and Heats of Solvation for Various lonophors in Water (kj/mol)... 

On the other hand, Arnett and his coworkers have reported both the enthalpies of the protonation (AHJ and the hydrogen bond (AHf) for acid-base reactions. They calculated Hj by measuring the association constants for the proton transfer (ionization) in a number of bases by using FSO3H as the acid and determined Ai/j by calorimetric measurements of the heat of dissolution of P-FC6H4OH in various hydrogen bond acceptors, including sulphoxides, in They have also tried to correlate and... 

The fundamental concept of heat transport controlled moisture uptake [17] is shown in Eq. (22), where the rate of heat gained at the solid/vapor surface (W AH) is balanced exactly by the heat flow away from the surface (Q). The term All is the heat generated by unit mass of water condensed on the surface. The two most probable sources of heat generation are the heat of water condensation and the heat of dissolution. A comparison of the heat of water condensation (0.58 cal/mg water) with the heat of dissolution for a number of salts indicates that the heat of dissolution can be neglected with little error for many materials. 

C.E. presumably affects also some experimental results on the ys. In particular, the effect of particle size on vapor pressure and solubilities, Sections III.6 and III.7, are related to C.E. more than to the true surface energy as already pointed out, small particles usually have a less perfect crystal lattice than do larger crystals. A more direct estimate of C.E. is afforded by the measurements of the heat of dissolution. 

The area of a MgO powder was determined from its gas adsorption capacity and its heat of dissolution was taken from the literature173. The t/s appeared to be about 1000 erg/cm2. 

Round sodium chloride particles of 0.2 mm in diameter were prepared by rapid cooling of droplets of a NaCl melt175). Their heat of dissolution in water exceeded that of large crystals by about 0.3% only. Consequently, the precision of the Us values was low the results of 3 pairs of experiments ranged from 4000 to 30000 erg/cm2. This high range may have been caused by the fact that the minute spheres were far from internal equilibrium. 

The heat of vaporization or the heat of dissolution has been incorporated in the term Neglecting the... 

Calculate the heat of hydration of NaCl and KCl from the following experimental data. The heat of sublimation for NaCl is 185.0 and that for KCl is 169.2 kcal/ mol the heat of dissolution for NaCl is 1.3 and that for KCl is 4.4kcal/mol. 

Americium and californium have been prepared by the reduction, using noble metals and hydrogen at temperatures greater than 1110 °C, of the oxides MOj 5. A new determination has been made of the heat of dissolution of Am in aqueous HCl, and the standard enthalpies of a series of Am compounds and ions have been reported (Table 1). The standard electrode potential of the Am -Am" couple was +2.06 + 0.01 V, making the metal only slightly more electropositive than Pu. 

Draw curves of the solubilities of the indicated salts. What relation can be noted between the heat of dissolution of a substance and the change in its solubility with the temperature ... 

Nitrosulphonic anhydride is a white, crystalline solid, of density 2-14. On heating it undergoes partial decomposition 7 it begins to melt at 217° C. to a yellow liquid and distils at about 860° C. The heat of formation, calculated from the heat of dissolution in potassium hydroxide, is 112 Calories ... 

The heat of formation of liquid arsenic trifluoride has been obtained 1 indirectly by determining the heats of dissolution of the trifluoride and of a mixture of arsenious oxide and sodium fluoride in about one litre of normal sodium hydroxide solution. The value obtained was 198,300 calories. Assuming Trouton s constant to be 21, the heat of vaporisation is about -7000 calories, so that the heat of formation of gaseous arsenic trifluoride is 191,300 calories. 

Increase in temperature causes a slight decrease in refractive index. The heat of dissolution 4 of the octahedral form is - 7530 calories at 18° C. The velocity of crystallisation from supersaturated solutions corresponds with 5 - dcjdt = fre4, where c is the concentration the temperature coefficient for the interval 0 to 25° C. is zero. 

Arsenic pentoxide is a white amorphous powder of density 5 3-7 to 4-3. It is tasteless when first introduced into the mouth, but rapidly becomes sharp and bitter and exerts a toxic action 6 similar to that of arsenious oxide (see Chapter XI), probably owing to the formation of the latter by reduction. The heat of formation (2As, 50) is 218,300 calories,7 and (As203, O,) 64,710 calories 8 the heat of dissolution (As2Os, aq.) is 6000 calories. 

The following values for the heats of neutralisation at 15° C. of arsenic acid by aqueous ammonia, and for the heats of dissolution of the ammonium arsenates, have been obtained.2 The solutions of arsenic acid for the determination of the former contained J mole of H3As04 per litre, and those of ammonia were of such concentrations that 1 volume of the acid was neutralised by an equal volume of the base. 

From the above data, and assuming the heat of dissolution of arsenic pentoxide to be + 6000 calories (see p. 180), the following values for the heats of formation have been ealeulated 3... 

When crystals of this material are placed upon the tongue, something happens, but a taste panel that was established cannot say just what. They agreed, however, that the compound is tasteless. Possibly the panel responds to a sense of coldness because of the heat of dissolution of the compound. 

On the basis of observations made on limited structural series, certain authors (e.g., Adamson, 1980) suggested that water absorption would occur by occupancy of the available free volume by water molecules. Despite its seductive intuitive character, this theory fails to explain why free-volume rich substances such as silicone rubbers, crosslinked polyethylene, or simply liquid aliphatic hydrocarbons are hydrophobic. Furthermore, experimentally determined apparent heat of dissolution values (Hs) and plasticization effects generally agree well with theoretical predic-... 

Ogg [98] studied the heat of dissolution of nitric anhydride is water, and on the basis of the results obtained came to the conclusion that the compound underwent the following reactions (a), (b), (c) and (d) ... 

The heat of dissolution of alumina in molten cryolite, AHiis, varies with the alumina concentration, an average value [161] being AHiis = 125,000 J mol-1. When a large quantity of alumina is added to the bath, the heat needed for its heating from room temperature to the electrolyte temperature and the heat of dissolution are taken from the bath. For this reason, localized freezing occurs, with the formation of aggregates which tend to drop to the bottom of the cell. In this manner a sludge is formed [161]. 

The direct measurement of the heats of mixing of two polymers is not possible. Several authors have attempted to measure the heats of mixing in the presence of a solvent, using Hess s law to extract the heat of mixing of the polymers In order to do this one needs to measure the heats of dissolution of the base polymers and of the blend in a common solvent. Some workers have said that this technique should be confined to rubber samples since glasses are not at equilibrium and results depend on the history of the glassy samples In principle this is a very attractive... 

Seivert s law is valid because gaseous hydrogen can be considered an ideal gas and H2 molecules are dissociated into atoms before becoming dissolved in metals [15]. Figure 4.2 presents the heat of dissolution for alkali, alkaline earth, and transition metals. 

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