High dilution calorimetric determination of the standard state thermodynamic differences between the properties of H +(aq) and Na +(aq) up to 598.15 K

Abstract

Standard state thermodynamic properties for fully ionized aqueous perrhenic acid at temperature in the range of (298.15 to 598.15) K and at p sat were determined by high dilution solution calorimetry (10 −4 m). A comparison of the standard state thermodynamic properties for fully ionized aqueous perrhenic acid, HReO 4 ( aq ) , and sodium perrhenate, NaReO 4 ( aq ) , establishes for the first time the quantitative values for the differences between H + ( aq ) and Na + ( aq ) from temperature of (298.15 to 598.15) K. Perrhenic acid is believed to be the first strong acid to be thermodynamically well characterized under standard state conditions to date from measurements down to 10 −4 m. The value of the Debye–Hückel limiting slope for enthalpies of dilution at temperature of 596.30 K of 122 ± 6 kJ · mol −3/2 · kg 1/2, obtained from the integral heats of solution measurement at various concentrations, is in good agreement with theoretical value in literature, 121 kJ · mol −3/2 · kg 1/2. This agreement verifies that HReO 4 ( aq ) obeys the simple limiting law for strong electrolytes. Many thermodynamic properties of soluble sodium electrolytes can now be converted to the corresponding acid form.