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Volume 141,number I,2 CHEMICAL PHYSICS LETTERS 30 October 1987 NEW APPROXIMATE LIMITING LAWS
 

Summary: Volume 141,number I,2 CHEMICAL PHYSICS LETTERS 30 October 1987
NEW APPROXIMATE LIMITING LAWS
FOR ACTIVITY AND RATE COEFFICIENTS OF IONS IN SOLUTION
Noam AGMON
Department of Physical Chemistry, The Hebrew University,Jerusalem 91904, Israel
Received 5 August 1987
A new approach is present for concentration effects on ionic reactions in solutions of small electrolyte concentrations. It is
assumed that the mutual Coulomb interaction is felt by an ion pair only when their separation is smalller than the "Coulombic
horizon", R.,, namely when there is no intervening ion. This leads to an approximate but simple and parameterless, formula for
activity coefftcients, with a cube root dependence on concentration in this regime. Steady-state diffusional rate coefficients are
calculated to and from the sphere at R,,. Comparison made with experimental activity coefticients of strong and weak electrolytes
shows that the upper validity limit of the new formula exceeds that of the Debye-Htickel limiting law. The diffusional rate con-
stant from R., gives a reasonable description of the concentration dependence of the ionic association rate coefficients, for con-
centrations where the Bronsted-Bjerrum limiting expression ceases to apply.
1. Introduction
Due to the long range of the Coulomb interaction,
both rate and equilibria of ionic reactions in solution
are substantially influenced by ionic concentration
[ l-151. In very dilute solutions, one obtains the
Debye-Hilckel limiting law [ 11. This is confirmed

  

Source: Agmon, Noam - Institute of Chemistry, Hebrew University of Jerusalem

 

Collections: Chemistry