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Dielectric Shielding of Ionic Charges in Aqueous Solutions of Different Ionic Strength
Author(s) -
Fabbrizzi Luigi,
Paoletti Piero,
Zobrist Markus C.,
Schwarzenbach Gerold
Publication year - 1973
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19730560213
Subject(s) - chemistry , aqueous solution , dielectric , ionic bonding , dipole , ionic strength , molecule , enthalpy , electrolyte , ion , proton , thermodynamics , organic chemistry , physics , optoelectronics , electrode , quantum mechanics
Abstract The thermodynamic functions of the proton transfer H 2 tn 2+ +tn → 2 Htn + (tn = 1,3‐diaminopropane) have been determined in aqueous solutions containing different amounts of KCl (0.05 ⩽ μ ⩽ 3.01). The free energy (−ΔG) of the process decreases, whereas the enthalpy (‐ΔH) increases with μ. There is reason to believe that the reaction is entirely controlled by the Coulomb forces between the two protonic charges. The electrostatic energy involved can be described in terms of a model incorporating an effective dielectric constant εe, such that δε e /δμ and δ 2 ε e /δμδT are both positive. The polarisation of pure water is produced by orientation of hydrogen‐bonded dipole molecules H 2 O, whereas the electrolyte solution is polarised in addition by dislocation of the ions K + and Cl − . Our results demonstrate that the former type of polarisation is much more temperature dependent than the latter.