V. Pekárek

Enthalpy of crystallization of lithium chloride from aqueous solution at 25°C

The enthalpies of crystallization of LiCl and LiCl·H2O from aqueous solutions at 25°C are reported as measured by a calorimetric method and derived from the previously published concentration dependence of the enthalpy of solution data. The results are compared with those obtained from the concentration dependence of activity coefficients and from the temperature dependence of solubilities.

Crystallization Studies by Thermometric Methods

The effect of thermal history of a solution (i.e. time and temperature of overheating preceding the measurements) has been analyzed on a theoretical basis and described by semiempirical equations taking into account structural changes in solution but using only measurable quantities. Induction periods so estimated have been employed for predictions of the kinetics of nucleation under given experimental conditions. The spontaneous crystallization of a closed sample of supersaturated solution with defined thermal history has been studied using computer simulation and compared with direct measurements of KC103 crystallization in a Calvet microcalorimeter. The agreement of both these results is very good and stimulating for further studies.

The history of thermoanalytical and related methods in the territory of present-day Czechoslovakia

Abstract This article deals with the history, development and present state of thermal analysis and calorimetry in the territory of contemporary Czechoslovakia, starting from the preclassical period up to the present day. The most important contributions of Czechoslovak scientists and the activities of national thermoanalytical groups are both surveyed, including the genesis of scientific meetings and seminars.

Integral heat of dissolution of potassium chlorate in water at 298.15 K

Abstract The heat of dissolution of potassium chlorate in water at 298.15 K has been measured on an LKB 8700-1 calorimeter in the concentration range 0.063–0.659 m. The concentration dependence of the measured data was fitted by an empirical equation ΔHm (kJ mole−1) = 41.3538 + 1.8626m 1 2 − 6.4300m which was derived from our and Andauer—Lange data. The heat of crystallization calculated from this dependence was ΔHcryst. = 34.7 ± 0.5 kJ mole−1, which agrees with data calculated for potassium chlorate from solubility and activity data.

Enthalpies of solution and of crystallization of lithium nitrate and of lithium nitrate trihydrate in water at 25°C

The enthalpies of crystallization of LiNO3 and LiNO3−3H2O from aqueous solutions at 25°C, measured by a calorimetric method and determined from the previously published data on the concentration dependence of the enthalpy of solution, are reported. The results are compared with the values obtained from the concentration dependences of the activity coefficients and from the temperature dependences of the solubilities. The enthalpy of solution at infinite dilution and the enthalpy of hydration are given.

Concentration dependence of activity coefficients at saturation and at 298.15 K evaluated from heat of crystallization and solubility data

Abstract For inorganic electrolytes of AgNO 3 , CsNO 3 , KNO 3 , LiNO 3 ·3H 2 O, NaNO 3 , NH 4 NO 3 , RbNO 3 , TlNO 3 , KClO 3 , K 2 CrO 4 , K 2 Cr 2 O 7 , K 2 SO 4 and K 2 S 2 O 8 , the concentration dependence of activity coefficients at saturation is evaluated from heats of crystallization and from the temperature dependence of their solubilities. Calculated values are compared with those deduced from measured data. The degree of their mutual consistency differs considerably from case to case.

Enthalpy of mixing in KCl-KBr mixed crystals at 25°C

Abstract The enthalpy of mixing in KCl-KBr mixed crystals (molar ratios of 1:0.33, 1:0.63 and 1:1.79) was calculated from calorimetric measurements of integral dissolution enthalpies at 25 °C. The results are compared with experimental data reported in the literature and with values calculated by using different theories.

The enthalpies of solution and crystallization of sodium nitrate in water at 25°C

The differential enthalpies of solution of sodium nitrate in water have been measured calorimetrically at 25°C, from 0.5 to 10.4 mol (kg H2O)−1. The concentration dependence is described by the equation ΔH=20.4537+1.0562m1/2-7.0568m+2.8659m3/2-0.3382m2 From the calorimetric measurements, the enthalpy of crystallization of sodium nitrate was calculated as ΔHc=9.98±0.16 kL-mol-1. The literature data on the solubility, activity and osmotic coefficients of NaNO3 at 25°C yielded a value of −9.98±0.38 kJ-mol−1. The good agreement between the experimental and calculated ΔHc values indicate the reliability of the input data.

Enthalpies of crystallization and dissolution of ammonium bromide in water at 298.15 k

Abstract The enthalpy of dissolution of ammonium bromide in water at 298.15 K was measured over the concentration range 0.01–7.2 mol NH 4 Br/1 kg water using three different calorimeters in two laboratories. The results obtained at low concentrations are compared with published values. The concentration dependence of the differential enthalpy of dissolution near saturation is best fitted by the equation -Δ H = 19.3889−2.0654m 1 2 (m > 6.25 mol NH 4 Br/1 kg H 2 O). The enthalpy of crystallization at the saturation concentration 7.968 mol NH 4 Br/1 kg H 2 O was found to be 13.55 ±0.05 kJ mol −1 . This result is compared with values calculated from published solubility data and from the concentration dependence of the osmotic coefficient at saturation.

Enthalpy of dissolution of lici and LiCl·H2O in water at 25° C at low concentrations

Abstract Enthalpy of dissolution of LiCl and LiCl·H2O in water was measured at 25° C at low concentrations. The molar enthalpy of dissolution extrapolated to infinite dilution is ΔsH∞ (LiCl, 25° C) = −(37.11 ± 0.35) kJ mol−1 LiCl. The published values of ΔsH∞ for both compounds were critically assessed and their reliability discussed. The comparison of measurements of previous authors reveals unidentified calorimetric errors.