The Debye-Huckel Theory of Strong Electrolytes

Measurement of the potential by means other than electro-kinetic measurement. G. S. Hartley and J. W. Roe1 point out that the potential determines the distribution of ions near a surface in the same manner as the potential just outside an ion controls the ionic atmosphere in the Debye-Huckel theory of strong electrolytes. There is a simple relation between the concentration of an ion in the layer next to a surface and in the bulk solution at a distance from the surface and the potential, so that if a means can be found of measuring the concentration of an ion in the surface and in the solution, it should be possible to estimate the potential of that surface. 

Kirkwood, J. G. and Poirier, J. C., The statistical mechanical basis of the Debye-Huckel theory of strong electrolytes. J. Phys. Chem. 86, 591-596 (1954). 

Mechanical Basis of the Debye-Huckel Theory of Strong Electrolytes. 

Theoretical investigations lead to the conclusion that there is a far going analogy between the structure of the double layer and that of the Debye-Huckel ionic atmospheres, In fact, considerations of this kind on the double layer arc older than the Debye-Huckel theory of strong electrolytes. 

Battery electrolytes are concentrated solutions of strong electrolytes and the Debye-Huckel theory of dilute solutions is only an approximation. Typical values for the resistivity of battery electrolytes range from about 1 ohmcm for sulfuric acid [7664-93-9] H2SO4, in lead—acid batteries and for potassium hydroxide [1310-58-3] KOH, in alkaline cells to about 100 ohmcm for organic electrolytes in lithium [7439-93-2] Li, batteries. 

Then, about 1904, it was pointed out by A. A. Noyes in this country and Sutherland in England that many properties of solutions of salts and strong acids (such as their color) suggest that most salts and strong acids are completely ionized in dilute solution. This view has been generally accepted since 1923, when a quantitative theory of the interactions of ions in solution was developed by Debye and Hiickel. This theory is called the Debye-Huckel theory of electrolytes. 

The Debye-Huckel theory is accurate in solutions in which the interactions between ions are not too great (i.e., at low ionic strengths in solutions of monovalent ions in solvents with large dielectric constants). In Fig. 2, the predictions of Eq. (21) are compared with experimental data for some strong electrolytes with different ionic charges. 

It will be observed that in the preceding treatment the assumption has been made that the ion concentration is in each case the same as the total concentration of the electrolyte. That is to say, a degree of dissociation has not been introduced. For this reason the Debye-Huckel theory has been frequently referred to as a theory of complete dissociation. Although the evidence, Chapters 8 and 12, appears to support the assumption that at least in dilute aqueous solutions strong... 

Lewis and Randall (Ref. [99]) introduced the term ionic strength, defined by this equation, two years before the Debye-HUckel theory was published. They found empirically that in dilute solutions, the mean ionic activity coefficient of a given strong electrolyte is the same in all solutions having the same ionic strength. 

Having dealt with activities and activity coefficients in solutions made up from strong electrolytes, we now turn to the determination of in weak electrolytic solutions. For this purpose we discuss some applications of the Debye-Huckel theory. 

Peter Joseph William Debye (1884-1966) was a Dutch-American physicist and physical chemist who was awarded Nobel Prize in Chemistry in 1936. He has a number of siguificant scientific contributions and one of them was the development of a theory of strong electrolyte solutions. The theory was created together with his assistant Erich HUckel and is known as Debye-Huckel theory. 

Apart from the above mentioned calculations on the /-potential, considerations on the structure of the electrical double layer have been mainly centred around the location of the ionic components. The treatment of the partition of the ions resembles very much the treatment of the ionic atmospheres in the theory of strong electrolytes. Remarkably enough the theoretical treatment of the double layer at a plane intc cc is older than the theory of Debye and Huckel and was first given independently by Gouy and Chapjaan... 

Debye-Huckel theory assumes complete dissociation of electrolytes into solvated ions, and attributes ionic atmosphere formation to long-range physical forces of electrostatic attraction. The theory is adequate for describing the behaviour of strong 1 1 electrolytes in dilute aqueous solution but breaks down at higher concentrations. This is due to a chemical effect, namely that short-range electrostatic attraction occurs... 

Debye-Huckel theory phys chem A theory of the behavior of strong electrolytes, according to which each ion is surrounded by an ionic atmosphere of charges of the opposite sign whose behavior retards the movement of ions when a current is passed through the medium. do bT hik-ol, the-3-re ... 

Debye-Huckel-Onsager theory — (- Onsager equation) Plotting the equivalent conductivity Aeq of solutions of strong electrolytes as a function of the square root of concentration (c1/2) gives straight lines according to the - Kohlrausch law... 

Debye-Huckel theory. A theory advanced in 1923 for quantitatively predicting the deviations from ideality of dilute electrolytic solutions. It involves the assumption that every ion in a solution is surrounded by an ion atmosphere of opposite charge. Results deduced from this theory have been verified for dilute solutions of strong electrolytes, and it provides a means of extrapolating the thermodynamic properties of electrolytic solutions to infinite dilution. 

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