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The enthalpy of formation of magnesium sulfate ion pairs

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Abstract

The enthalpies of dilution of lithium, sodium, potassium, and magnesium chloride and sulfate solutions in the range 0.1 to 1.0 m have been measured at 30°C with a microcalorimeter. The relative apparent enthalpies φL of these solutions have been determined with the aid of an extended form of the Debye-Hückel limiting law

$$\phi _L = S_H I^{1/2} [1/(1 + I^{1/2} ) - (\sigma /3)] + {\rm B}{\rm I} + CI^{3/2} $$

whereS H is the limiting-law slope, σ = 3/I3/2 × [(1+I1/2 − 1/(1+I1/2 − 2 ln (2+I1/2)], andB andC are empirical constants. This equation fits the experimental results to within a standard deviation of 2 cal-mole−1 for all the salts. The measured φL for the MgSO4 solutions were compared to those calculated using the additivity principle, φL(MgCl2) + φL(Na2SO4) − 2φL(NaCl), and the extended Debye-Hückel equation. The results of this comparison have been used to calculate the ΔH oA for the formation of MgSO 04 . A value of ΔH oA = 1.15 to 1.36 was obtained, depending upon the φL estimates for the free ions Mg2+ and SO 2−4 . The results are briefly discussed and compared to the results obtained by other workers.

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Authors and Affiliations

  1. Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, 33149, Miami, Florida

    Wing H. Leung & Frank J. Millero

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  1. Wing H. Leung
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  2. Frank J. Millero
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Taken in part from the Ph.D. Thesis of W. H. Leung, University of Miami, Miami, Florida.

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Leung, W.H., Millero, F.J. The enthalpy of formation of magnesium sulfate ion pairs. J Solution Chem 4, 145–159 (1975). https://doi.org/10.1007/BF00649155

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  • DOI: https://doi.org/10.1007/BF00649155

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