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|標題:||A unified model for predicting the mononuclear first- to fifth-order and the polynuclear hydrolysis constants of metal cations||作者:||Chang, C.M.
|關鍵字:||metal cation mononuclear;polynuclear;hydrolysis constant;ionization;energy;bond energy;reactant-stabilizing enthalpy coefficient;solution interface;surface-acidity;sites||Project:||Journal of Molecular Structure-Theochem||期刊/報告no：:||Journal of Molecular Structure-Theochem, Volume 664, Page(s) 21-26.||摘要:||
This contribution introduces a quite simple method to establish a universal equation for quantitatively estimating the cationic hydrolysis tendency in water. The unified model is constructed on the basis of the general from of the hydrolysis reaction of metal cations: mMe(Z+) + nH(2)O --> Me-m(OH)(n)((mZ-n)+) + nH(+). According to this general form, the metal cation (MeZ+) and water molecule (H2O) are properly regarded as the main reactants of a hydrolysis reaction of metal cations. The universal predicting equation for the thermodynamic hydrolysis constants (log K-mn) can then be obtained as: log K-mn = Omega(R-S) x (n/m) X (mIE + n BE) - (m + n)log 55.51 + (-DeltaGdegrees(Extra)/2.303RT)(n + 1)/2. The parameter IE is the total ionization energy of metal atoms. The parameter BE can be calculated from the energy change of the following reaction: oxygen atom + 2 hydrogen atom - water molecule. The enthalpy for stabilizing the hydrolysis reactants in an aquatic system is defined as Omega(R-S) x (n/m) x (mIE + nBE). Here Omega(R-S) is the reactant-stabilizing enthalpy coefficient, which equals the inverse of (2.303RT x dielectric constant of water). The entropy contribution for stabilizing the hydrolysis reactants in an aquatic system can be represented by the total molar numbers of the hydrolysis reactants, (m + n), multiplied with -log55.51. The remaining free energy term, (-DeltaGdegrees(Extra)/2.303RT), accounts for the extraneous effects arisen from adjacent solvent molecules interacting with the metal cation. This unified model finds out a physically meaningful coefficient (i.e. reactant-stabilizing enthalpy coefficient, Omega(R-S)) and proposes a novel free energy partioning procedure to make the universal prediction for cationic hydrolysis constants become possible. (C) 2003 Elsevier B.V. All rights reserved.
|Appears in Collections:||土壤環境科學系|
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