In this study, we investigated the mechanistic features and kinetics of the thermal decomposition of solids accompanied by liquefaction as exemplified by the thermal dehydration reactions of monosodium L-glutamate monohydrate...

When linearly heating trehalose dihydrate (TH-DH) at a relatively high heating rate (β ≥ 1.5 K min–1), the thermal dehydration begins in the solid state and transitions to the liquid state at the melting point of TH-DH (∼370 K). The complex mass loss and phase change characteristics observed during the thermal dehydration is due to the contributory effects of various physical phenomena, including melting of TH-DH and anhydride products. The reactions entirely occurred in the solid state under isothermal and nonisothermal conditions at a low heating rate (β ≤ 1.0 K min–1), and its kinetics were described by the physico-geometrical consecutive process comprising the surface reaction and subsequent phase boundary-controlled reaction. The reactions initiated at approximately the melting point of TH-DH under a significantly high atmospheric water vapor pressure and proceeded mostly in the liquid state exhibiting a single-step mass loss behavior. The thermal dehydration accompanied by liquefaction demonstrated an autocatalytic kinetic behavior, which was regulated by the evaporation of the water vapor from the surface of viscous liquid particles. The kinetic findings for the reactions in the solid and liquid states allow the physico-geometrical interpretation for the complex mass loss and phase change behaviors during heating TH-DH at relatively high β values.

In this laboratory experiment, a guided inquiry exploring the physicochemical principles of the dissolution of Ca(OH)2(s) in water is proposed for laboratory classes in university and high school. As part of students’ inquiry, two experimental approaches are used. One is the change in solubility with temperature revealed by measuring the pH values of the suspended solution of Ca(OH)2(s) at various temperatures, which is then extended to its thermodynamic relationship via examining the temperature dependence of the solubility constant. The other method is to determine the enthalpy of solution using the calorimetric measurements. Due to the poor solubility of Ca(OH)2(s), for determining the enthalpy of the Ca(OH)2(s) solution, development of an energy diagram composed of several paths of a reaction that involve the dissolution of Ca(OH)2(s) as a component process and using Hess’s law are essential. A combination of these experimental approaches yields a stepwise students’ inquiry for revealing the source of the changes in Ca(OH)2(s) solubility with temperature, which may be flexibly adapted as an appropriate program depending on the targeted students. The two experimental procedures are presented by critically examining the experimental results. Based on the results of educational practices, typical guided inquiry constructions suited for the university and high school chemistry courses are proposed.

Physico-geometrical reaction pathway and kinetics of the thermal dehydration of D-glucose monohydrate (DG-MH) dramatically alter by the melting of the reactant midway through the reaction. By controlling the reaction conditions,...