Vapour pressure of solute

The vapour pressure of the solution at the freezing-point is equal to that of pure ice at the same temperature (Guldberg, 1870). For if we take the system ice, solution, vapour, at the freezing-point, and suppose that p p" are the vapour pressures of solution and ice, , v" the specific volumes of the vapour under these pressures, and V, V" the specific volumes of solution and ice, we may execute the following isothermal cycle ... 

Biltz 4 carried out a series of investigations on the vapour pressures of solutions of silver chloride and ammonia, and came to the conclusion that silver chloride forms the triammine, [Ag(NH3)3]Cl, at atmospheric pressure below 20° ., and the sesquiammine, 2AgCl(NH3)3, at temperatures between 20° and 60° C. Above 00° C. silver chloride does not unite with ammonia. 

The vapour pressure of solutions of nitroglycol in nitroglycerine has been reported on p. 44 (Table 13). 

Measurements of the vapour pressures of solutions of nitric acid in ether carried out by Dalmon and his co-workers confirmed the existence of the compound. It was shown that the vapour pressure of ether, which at 0°C was 185 mm Hg, decreased on addition of nitric acid and attained 1 mm Hg when equimolar proportions of the two components were present in the solution. 

Bawn, C. E. H. Patel, R. D., "High Polymer Solutions. Part 8. The Vapour Pressure of Solutions of Polyisobutene in Toluene and Cyclohexane," Trans. Faraday Soc., 52, 1664 (1956). 

The transport method has been used for the determination of the vapour pressure of solutions, and in this case many precautions are necessary to obtain good results. Regnault found that liquids exert a lower vapour pressure in the presence of indifferent gases than in the presence of their own saturated vapour alone. This result was confirmed by Shaw, and by Campbell. The idea that vapour pressure corresponds with solubility in a vacuumis useful here. 

The vapour pressures of solutions have been determined. ... 

Vapour pressure of solutions. The Clausius equation can be applied directly to the evaporation of a solution if we make the restriction that the concentration of the solution shall not alter appreciably when 1 mol. of the solvent is evaporated, which is the case if we are dealing with a very large volume of the solution. The system solution-vapour is then monovariant, and has a definite vapour pressure p at every temperature. If the dissolved substance (solute) has no appreciable vapour pressure, this pressure p is equal to the partial pressure of the solvent. If not, the vapour pressure is equal to the total pressure, i.e. to the sum of the partial pressures of all the components of the solution. In the meantime we shall restrict ourselves to the first case. 

The relative lowering of the vapour pressure of solutions of the same concentration in different solvents is directly proportional to the molecular weight of the solvent, i.e. inversely proportional to the number of molecules of solvent in the solution. 

Dilute solutions. As has already been stated (p. 266), the relationship between the osmotic pressure of a solution and the concentration and chemical character of solvent and solute cannot be derived from purely thermodynamical considerations. There are several ways of attaining this end. In the first instance, the variation of the osmotic pressure with the concentration can be determined experimentally, and the results embodied in an empirical equation of the form p=/(c). Or we may deduce relationships from kinetic conceptions of the nature of solutions, in much the same way as the gas laws were deduced. Or, finally, we may deduce the osmotic pressure laws, with the aid of the thermodynamical equations of the previous paragraph, from empirical or theoretical researches on the vapour pressure of solutions. These methods all lead to the same result, that the osmotic pressure of dilute solutions obeys the same laws as the pressure of a perfect gas. In other words, the osmotic pressure of a substance in solution is equal to the pressure which the substance would exert in the form of a perfect gas occupying, at the same temperature, the volume of the solution. 

The vapour pressures of solutions of lithium in mcthylamine have been determined from 218 to 278 K, The activity of the amine showed positive deviations from Raoult s law at low metal concentrations and negative deviation with increasing concentration as in metal-ammonia solutions. The system was considered to contain solvated metal atoms coexisting with free MeNH molecules. ... 

To compare the vapour pressure of solutions of rubber in benzene with the Flory-Huggins formula. 

The vapour pressure of solutions of rubber in benzene has been measured at 25 C bj Gee and his collaborators (Gee and Treloar, Trans. Faraday Soc. 1942, 38,147 Gee and Orr, Trans. Faraday Soc. 1946,42, 507 supplemented by private communication from Dr. Gee). Values of the ratio of the vapour pressure f of the solution to the vapour pressure of pure benzene for various values of the volume fraction q> of rubber are given in table 1. 

EXERCISE 36 frobiMmon Vapour Pressures of Solutions of Two Liquids... 

Fig. 6.76 a Relationship between the relative dynamic modulus of elasticity and the degree of saturation of concrete after six fieezing and thawing cycles. (After [322]). b H O system O A curve corresponding to the vapour pressure of solution, OD curve corresponds to the vapour pressure of the supercooled water... 

G. R. Kirchhoff and J. Loschmidt made some important applications of the second law of thermodynamics to the vapour pressures of solutions, including the calculation of the work of isothermal distillation. F. KolaCek found a relation between the lowering of vapour pressure and depression of freezing-point, based on the second law of thermodynamics, and deduced an equation which gives Raoult s formula for the lowering of vapour pressure for very dilute solutions. Van t Hoff deduced equation (5) from thermodynamics. 

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