Solutes gaseous

Towers. Towers are required to provide retention times from 30 minutes, as in the chlorination and hypochlorite stages, to as much as five hours in some chlorine dioxide stages. Upflow and downflow towers are common. Upflow towers are often used for medium consistency stages. These are particularly advantageous when a hydrostatic head must be maintained on a gaseous solution, as in chlorine dioxide stages. 

All gas mixtures are homogeneous hence all gas mixtures are solutions. Air is an example. There is only one phase—the gas phase—and all the molecules, regardless of the source, behave as gas molecules. The molecules themselves may have come from gaseous substances, liquid substances, or solid substances. Whatever the source of the constituents, this gaseous solution, air, is a single, homogeneous phase. As with other solutions, the constituents of air are separated by phase changes. 

The first term inside the brackets evidently is the energy of a solute molecule J in the perfect gas (cf. Eq. 10) hence we have for the energy of formation of the clathrate from and the gaseous solute at constant volume per molecule of Q... 

For the gas hydrates it is not possible to make an entirely unambiguous comparison of the observed heat of hydrate formation from ice (or water) and the gaseous solute with the calculated energy of binding of the solute in the ft lattice, because AH = Hfi—Ha is not known. If one assumes AH = 0, it is found that the hydrates of krypton, xenon, methane, and ethane have heats of formation which agree within the experimental error with the energies calculated from Eq. 39 for details the reader is referred to ref. 30. 

GASEOUS SOLUTES 0 ARGON A NITROGEN O METHANE 0 HYDROGEN 9 SULFUR OlOXlDE... 

FIg. 6. Partial molar volumes of gaseous solutes at infinite dilution in expanded solvents. 

In the previous sections, we emphasized that at constant temperature, the liquid-phase activity coefficient is a function of both pressure and composition. Therefore, any thermodynamic treatment of gas solubility in liquids must consider the question of how the activity coefficient of the gaseous solute in the liquid phase varies with pressure and with composition under isothermal conditions. 

In the case, however, of solid solutions where variability of composition is possible we may expect increased entropy owing to the possibilities of increased randomness of arrangement just as with liquid and gaseous solutions. Also, other special cases might arise where a greater degree of randomness would be possible than in pure, perfect crystals, but such cases could be given a special treatment and would cause no confusion. 

A solution is a homogeneous mixture of two or more substances. As described in Chapter 3, a solution contains a solvent and one or more solutes. The solvent determines the state of the solution, and normally the solvent is the component present in the greatest quantity. The most common solutions are liquids with water as solvent, but solutions exist in all three states of matter. The atmosphere of our planet, air, is a gaseous solution with molecular nitrogen as the solvent. Steel is a solid solution containing solutes such as chromium and carbon that add strength to the solvent, iron. 

Gaseous solutions are easy to prepare and easy to describe. The atoms or molecules of a gas move about freely. When additional gases are added to a gaseous solvent, each component behaves independently of the others. Unless a chemical reaction occurs, the ideal gas equation and Dalton s law of partial pressures describe the behavior of gaseous solutions at and below atmospheric pressure (see Chapter 5). 

A convenient concentration measure for gaseous solutions is the mole fraction, introduced in Section 5-. The mole fraction (X, dimensionless) is the number of moles of one component divided by the total moles of all. Moles of A... 

Fig. 1.6 Absorption spectrum for water (gaseous, solution, and liquid). Above the vapor band is Mecke s rotational analysis [11,12].

For many gaseous solutions, even if the gases are not ideal, the partial molar volumes of the components are equal to the molar volumes of the pure components at the same total pressure. The gases are said to obey Amagat s mle, and the volume change on mixing is zero. Under these conditions, the gaseous solution behaves ideally in the sense that it obeys the equation... 

The fugacity coefficient y, of a constituent of a gaseous solution is defined by the expression... 

The Gibbs energy change for the process of dissolution of the gaseous solute B, Asoi Gb, is the driving force for the material transfer. When equilibrium is reached, Asoi Gb becomes zero (since, at equilibrium, no more net transfer occurs). The following equation then holds ... 

Whether obtained from an actual experimentally feasible process or from a thought process, As i Gg, which is obtained from Eq. (2.9) by re-arrangement, pertains to the solvation of the solute and expresses the totality of the solute-solvent interactions. It is a thermodynamic function of state, and so are its derivatives with respect to the temperature (the standard molar entropy of solvation) or pressure. This means that it is immaterial how the process is carried out, and only the initial state (the ideal gaseous solute B and the pure liquid solvent) and the final state (the dilute solution of B in the liquid) must be specified. 

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