Concept explainers
The article “Enthalpies and Entropies of Transfer of Electrolytes and Ions from Water to Mixed Aqueous Organic Solvents” (G. Hefter. Y. Marcus, and W. Waghorne, Chemical Reviews, 2002:2773–2836) presents measurements of entropy and enthalpy changes for many salts under a variety of conditions. The following table presents the results for enthalpy of transfer (in kJ/mol) from water to water + methanol of NaCl (table salt) for several concentrations of methanol. Hour independent measurements were made at each concentration.
Concentration (%) | Enthalpy | |||
5 | 1.62 | 1.60 | 1.62 | 1.66 |
10 | 2.69 | 2.66 | 2.72 | 2.73 |
20 | 3.56 | 3.45 | 3.65 | 3.52 |
30 | 3.35 | 3.18 | 3.40 | 3.06 |
- a. Is it plausible that the enthalpy is the same at all concentrations? Explain.
- b. Which pairs of concentrations, if any, can you conclude to have differing enthalpies?
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