Impact of atmospheric water vapor pressure on the kinetics of the thermal decomposition of Ca(OH)2 can be described universally.

Kinetic features of the thermal decomposition of Mg(OH)2 are revealed under different heating and water vapor pressure conditions.

The thermal decomposition of Mg­(OH)2 was selected to realize an integrated kinetic understanding of the thermal decomposition of inorganic solids by correlating the physico-geometrical mechanisms and the effect of the product gas presented in the reaction atmosphere. Herein, the mechanistic features of the reaction, as revealed by a systematic kinetic study on a reaction in flowing dry N2 gas, were reported as the first part of the study. In spite of the smooth mass loss under various heating conditions, the formal kinetic analysis based on an assumption of single-step reaction indicated a possible multistep reaction comprising the surface reaction (SR) and subsequent internal phase boundary-controlled reaction (PBR). Two physico-geometrical models were applied to find the mechanistic features of the overall reaction. One is a single reactant-body model with an assumption of independent SR and PBR. The other is based on the physico-geometrical consecutive SR–PBR model in the assemblage of reactant particles. Through the stepwise kinetic analyses on these models, the SR and PBR were characterized by the first-order kinetic law with an activation energy (E a) of approximately 130 kJ mol–1 and two- or three-dimensional interface shrinkages with an E a value of approximately 248 kJ mol–1, respectively.

Thermally induced carbonation of Ca(OH)2 in a CO2 atmosphere is a reaction exhibiting particular features, including stoichiometric completeness to form CaCO3 and a kinetic advantage over the carbonation of CaO particles.

This study focuses on designing a laboratory learning program for a high school chemistry course in which students could discover the fundamental principles of Hess's law via stepwise inquiry. By exploring the chemical properties of common desiccants, mainly those that were reactive in water, students were introduced to the exothermic reaction of CaO(s) with H 2 O(l) as a heating agent. Due to the difficulties associated with directly measuring the heat of reaction for CaO(s) with H 2 O(l), the heats of reaction for CaO(s) with HCl(aq) and Ca(OH) 2 (s) with HCl(aq) were measured. Students could find the most appropriate experimental procedures through discussion in each group and subsequently establish a protocol in the class. The heats of reaction determined by students' experiments closely corresponded to those calculated using the thermodynamic database. Using the experimental values obtained for the reactions of CaO(s) with HCl(aq) and Ca(OH) 2 (s) with HCl(aq), students could discover the relationship that existed among the heats of reaction for CaO(s) with H 2 O(l), CaO(s) with HCl(aq), and Ca(OH) 2 (s) with HCl(aq) by drawing an energy diagram and making the relevant thermochemical calculations.

This study focuses on the physico-geometrical constraints of the kinetics of the thermal decomposition of solids as exemplified by the thermal dehydration of α-oxalic acid dihydrate and the subsequent thermally...

A newly developed laboratory learning program for high school chemistry courses is discussed, in which students discover the chemical mechanism governing exothermic phenomena during the reaction between a heating agent, namely, calcium oxide (CaO)−aluminum (Al) mixture, and water. Based on prior knowledge of simple heating agents such as CaO, the students were able to accurately identify the component chemical reactions in the CaO−Al mixture and water system using three pairs of comparable thermometric measurements arranged in a stepwise manner. In each step, the students designed the comparative experiments for each student group through logical thinking and argumentation to obtain relevant and reliable results. Active interpretation of the results enabled each student to learn the chemical phenomena inherent in the observed reactions, and their understanding was deepened through evidence-based argumentation and debate. Finally, students in each group proposed an overall chemical mechanism governing the reaction between the CaO−Al mixture and water by consolidating the knowledge acquired during the previous inquiry steps. The proposed chemical mechanism was fine-tuned through group presentations, followed by question and answer sessions. The 6-h evidence-driven activity provided numerous opportunities for experiencing the multifaceted aspects of the scientific inquiry process.

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.