Activity of a solvent

The activity of a solvent can be determined in a solution from the change in the freezing temperature or the boiling temperature due to the addition of a solute. Consider a process in which a solution is cooled until solid (component 1) crystallizes from solution. An equilibrium is established so that... 

The present authors studied the solvolytic liquefaction process ( ,7) from chemical viewpoints on the solvents and the coals in previous paper ( 5). The basic idea of this process is that coals can be liquefied under atmospheric pressure when a suitable solvent of high boiling point assures the ability of coal extraction or solvolytic reactivity. The solvent may be hopefully derived from the petroleum asphaltene because of its effective utilization. Fig. 1 of a previous paper (8) may indicate an essential nature of this process. The liquefaction activity of a solvent was revealed to depend not only on its dissolving ability but also on its reactivity for the liquefying reaction according to the nature of the coal. Fusible coals were liquefied at high yield by the aid of aromatic solvents. However, coals which are non-fusible at liquefaction temperature are scarcely... 

The activities of pure liquids and solids are 1 the activity of a solvent in a dilute solution is approximately 1. 

The activity of a solvent is defined differently from that of a solute. The solvent is the species having the highest mole fraction in a solution mole fraction indicates the fraction of the total number of moles in a system contributed by that species. For a solvent, is yyiVy, where N - is its mole fraction. An ideal solvent has ysoivent equal to 1, meaning that the interactions of solvent molecules with the surrounding molecules are indistinguishable from their interactions in the pure solvent. An ideal solution has all activity coefficients equal to 1. 

In these expressions, and Aj represent, respectively, the number of solvent and of solute molecules, and the quantity % (or z ) is the absolute activity of a solvent (or solute) molecule and is related to the chemical potential. The configurational partition function which refers... 

When a condensable solute is present, the activity coefficient of a solvent is given by Equation (15) provided that all composition variables (x, 9, and ) are taicen on an (all) solute-free basis. Composition variables 9 and 4 are automatically on a solute-free basis by setting q = q = r = 0 for every solute. 

The discussion so far has been confined to systems in which the solute species are dilute, so that adsorption was not accompanied by any significant change in the activity of the solvent. In the case of adsorption from binary liquid mixtures, where the complete range of concentration, from pure liquid A to pure liquid B, is available, a more elaborate analysis is needed. The terms solute and solvent are no longer meaningful, but it is nonetheless convenient to cast the equations around one of the components, arbitrarily designated here as component 2. 

Although there are examples of enzymes which maintain their catalytic activity even when ciystallized, they normally work in their natural (i.e., aqueous) environment. This is the reason why the majority of the simulations are carried out applying a technique that accounts for solvent effects. But what is the effect of a solvent ... 

Osmotic pressure is one of four closely related properties of solutions that are collectively known as colligative properties. In all four, a difference in the behavior of the solution and the pure solvent is related to the thermodynamic activity of the solvent in the solution. In ideal solutions the activity equals the mole fraction, and the mole fractions of the solvent (subscript 1) and the solute (subscript 2) add up to unity in two-component systems. Therefore the colligative properties can easily be related to the mole fraction of the solute in an ideal solution. The following review of the other three colligative properties indicates the similarity which underlies the analysis of all the colligative properties ... 

Boiling point elevation. A solute which does not enter the vapor phase to any significant extent raises the boiling point of the solvent. As above, the solute lowers the activity of the solvent, which, in turn, lowers the vapor pressure. Therefore the solution must be raised to a higher temperature before its vapor pressure reaches 1.0 atm. At equilibrium... 

The hquid remaining after the solvent has been recovered is a heavy residual fuel called solvent-refined coal, containing less than 0.8 wt % sulfur and 0.1 wt % ash. It melts at ca 177°C and has a heating value of ca 37 MJ/kg (16,000 Btu/lb), regardless of the quaUty of the coal feedstock. The activity of the solvent is apparently more important than the action of gaseous hydrogen ia this type of uncatalyzed hydrogenation. Research has been directed to the use of petroleum-derived aromatic oils as start-up solvents (118). 

The apparent acid strength of boric acid is increased both by strong electrolytes that modify the stmcture and activity of the solvent water and by reagents that form complexes with B(OH) 4 and/or polyborate anions. More than one mechanism may be operative when salts of metal ions are involved. In the presence of excess calcium chloride the strength of boric acid becomes comparable to that of carboxyUc acids, and such solutions maybe titrated using strong base to a sharp phenolphthalein end point. Normally titrations of boric acid are carried out following addition of mannitol or sorbitol, which form stable chelate complexes with B(OH) 4 in a manner typical of polyhydroxy compounds. EquiUbria of the type ... 

Cesium forms simple alkyl and aryl compounds that are similar to those of the other alkah metals (6). They are colorless, sohd, amorphous, nonvolatile, and insoluble, except by decomposition, in most solvents except diethylzinc. As a result of exceptional reactivity, cesium aryls should be effective in alkylations wherever other alkaline alkyls or Grignard reagents have failed (see Grignard reactions). Cesium reacts with hydrocarbons in which the activity of a C—H link is increased by attachment to the carbon atom of doubly linked or aromatic radicals. A brown, sohd addition product is formed when cesium reacts with ethylene, and a very reactive dark red powder, triphenylmethylcesium [76-83-5] (C H )2CCs, is formed by the reaction of cesium amalgam and a solution of triphenylmethyl chloride in anhydrous ether. 

The preemulsified carriers contain water. These products usually require homogenization through colloidal mills or similar equipment to reduce the particle size and ultimately stabilize the product. The preemulsified as well as the clear self-emulsifying products require the use of a solvent when the carrier-active material is a soHd. 

Triethylbenzylammonium chloride and potassium fluoride containing 1% water can provide chlorine-fluorine exchange of activated halides in the absence of a solvent. This mixture also can displace the chlorine of a chlorodifluoromethyl group to form a trifluoromethyl group [62] (equation 36). 

The free energy of activation at the QCISD(T)/6-31 H-- -G(d,p) level amounts to 21.1 kcal/mol. According to the authors, the large electron density redistribution arising upon cyclization makes it necessary to use extended basis sets and high-order electron correlation methods to describe the gas-phase thermodynamics, which indicates clearly the gas-phase preference of the azido species. However, the equilibrium is shifted toward the tetrazole as the polarity of a solvent is increased. For instance, SCRF calculations (e = 78.4) yield a relative free energy of solvation with respect to the cw-azido isomer of —2.4 kcal/mol for the tmns-zziAo compound and of —6.8 kcal/mol for the tetrazole isomer. At a much lower level, the... 

Apart from the activation of a biphasic reaction by extraction of catalyst poisons as described above, an ionic liquid solvent can activate homogeneously dissolved transition metal complexes by chemical interaction. 

In solution polymerization, an organic solvent dissolves the monomer. Solvents should have low chain transfer activity to minimize chain transfer reactions that produce low-molecular-weight polymers. The presence of a solvent makes heat and viscosity control easier than in bulk polymerization. Removal of the solvent may not be necessary in certain applications such as coatings and adhesives. 

The chemical potential in the solution is related to the activity of the solvent a, by... 

The activity of a volatile solvent in a solution that contains a nonvolatile solute can be obtained from an experimental technique known as the isopiestic method .19 An apparatus is constructed similar to that shown in Figure 6.17. The mixture in container A is a solution of a nonvolatile solute in a solvent in which A], the activity of the solvent, has been accurately determined in other experiments as a function of concentration. Containers B and C hold solutions of other nonvolatile solutes in the same solvent. These are the solutions for which the activity of the solvent is to be determined. 

Most of the methods we have described so far give the activity of the solvent. Often the activity of the solute is of equal or greater importance. This is especially true of electrolyte solutions where the activity of the ionic solute is of primary interest, and in Chapter 9, we will describe methods that employ electrochemical cells to obtain ionic activities directly. We will conclude this chapter with a discussion of methods based on the Gibbs-Duhem equation that allow one to calculate activities of one component if the activities of the other are known as a function of composition. 

The osmotic coefficient is often used as a measure of the activity of the solvent instead of a because a is nearly unity over the concentration range where 7 is changing, and many significant figures are required to show the effect of solute concentration on a. The osmotic coefficient also becomes one at infinite dilution, but deviates more rapidly with concentration of solute than does a. ... 

On the isopotential map three minima (III, IV, V) are separated by barriers. They can be reached by decreasing of the distance R between the educts (I) via an activated complex (II). A detailed discussion of this potential energy surface also under the influence of a solvent will be given in part 4.3.1. 

Rabbit Ear Bioassay for Acnegenic Activity. Acnegenic activity of 2-7-DCDD, 1,2,3,4-TCDD, 2,3,7,8-TCDD, HCDD, and OCDD was tested by applying 0.1 ml of either a solvent solution or the supernatant of a solvent suspension of each compound to the inner surface of the rabbit s ears five days a week for four weeks. The ears were examined weekly for signs of chloracne, inflammation, and hyperkeratosis. The responses were divided into five categories (1) none, (2) very slight, (3) slight, (4) moderate, and (5) severe. 

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