The Gaseous Behaviour of Solutions

The Gaseous Behaviour of Solutions

Newton (1642 to 1727) regarded the repulsion between dissolved species to be similar to the diffusion of gas molecules. Gay-Lussac, in 1839, noted that dissolution is strongly related to the number of molecules which at a particular temperature are able to exist in a volume of solvent and that dissolution and evaporation are similar. Bizio, 1845, expressed opinions that dissolved substances behaved like elastic vapor in the solvent. Rosenstiehl, 1870, commented that osmotic force is analagous to the elastic force of a vapor and that there is no difference other than that of the medium in which the work is effected.

The laws for thermodynamic equilibria between gases had been deduced in the 1870's by Horstmann. He then found the equation also applied to the equilibrium between dissolved sulphates and carbonates of potassium and barium. The concept of osmotic pressure was known from studies on sugar cane. In 1877 Pfeffer measured the osmotic pressure of a 1 % cane suger solution and found it to be 505 mm of mercury at 6.8 degrees C. De Vries told van't Hoff of this result, and asked for an explanation of it. Van't Hoff calculated that this would be the same pressure for the same number of gas molecules (as cane sugar molecules) contained in the same volume as the volume of the solution.

Van't Hoff then applied all the thermodynamic laws for the pressure of gases and saturated vapours, which correspond to saturated solutions, to the osmotic pressure of dissolved substances. He found he was able to deduce: - The general law of chemical equilibria (Guldberg and Waage), - The law of influence of pressure on chemical equilibria (Le Chatelier), - The law of temperature effect on chemical equilibria , - The law of partition of substances between phases (Henry, Berthelot, Jungfleisch), - The law of vapour pressure and freezing point of solutions (Raoult), - The law of isotonic solutions (De Vries), - The law of partition of a base between two acids (Jellet, Thomsen, Ostwald), - The law of change of solubility with temperature (Guldberg), - The regularities in the action of water on salts (Ditte), - The law relating electromotive force of galvanic cells (introducing the concept of "free energy") (Gibbs and Helmholtz).

Arrhenius added that this all applied to the dissociated ions. Planck and Boltzmann, with their intellectual authority, supported the fledgling theory from marauding physicists during the early years.

All of this is according to the account of Arrhenius.

Cheers, Jim