A mathematical model is proposed to investigate the kinetics and equilibrium of homogeneous elementary first- and second-order chemical reactions. The dynamics is defined by the Monte Carlo method (MCM), with the Metropolis update, and the Ehrenfest urn model (EUM). MCM is an important step that accesses the kinetic and thermodynamic properties of the system, while the EUM defines the orders of the reactions studied in this work. The main parameters, such as temperature, the activation energy and the steric factor, were taken into account in the calculation of the transition probabilities between the reactants and products. It is thus possible to reproduce the kinetic profiles of the reactions and to evaluate the influence of temperature and the steric factor. Furthermore, it is possible to simulate the behaviour of the system by modifying the activation energy barrier, thus simulating a catalytic process. The effect of the addition of molecules was also investigated, with the system returning to a thermodynamic equilibrium condition after partial consumption of the added reactant, as predicted by Le Chatelier’s principle. All the simulated data are in agreement with the theoretical results present in physical chemistry textbooks.

This study aims to examine how structured the discipline of History of Science and Technology in the faculty of Chemistry, Faculty of Engineering - FIQ of the Universidad Nacional del Litoral - Santa Fe, Argentina, and how the teacher of the subject has adequate knowledge of History and Philosophy of Science for the teaching of this subject. It is emphasized that the course does not offer a discipline that studies the "History and Philosophy of Chemistry". The study presents a qualitative research approach in the framework, among those cited, referencing different authors Argentines and Brazilians. The data were collected from teachers using a semi-structured interview, course documentation and analytical program. The results obtained so far show the need to rethink the discipline by assigning a greater emphasis on science epistemological knowledge. The inclusion of aspects of History and Philosophy of Science can be considered as a key integrator to understand the specific contents of the subject to be taught and is one of the possible ways to improve the understanding of the nature of science. This study can help in discussions and curricular experiences of other universities including the discipline of History of Science and / or Chemistry in its curriculum.

Este estudio tiene como objeto examinar cómo se estructura la disciplina Historia de la Ciencia y Tecnología en la Facultad de Ingeniería Química - FIQ - de la Universidad Nacional del Litoral - Santa Fe, Argentina, y cómo el profesor de la asignatura tiene un conocimiento adecuado de Historia y Filosofía de la Ciencia para la enseñanza de la misma. Se hace hincapié en que la carrera no ofrece una disciplina que estudie la "Historia y Filosofía de la Química". El trabajo presenta un enfoque de investigación cualitativa y en este marco, se citan y referencian a diferentes autores argentinos y brasileños. Los datos fueron recolectados utilizando una entrevista semi-estructurada a los profesores, además del análisis de la documentación y el programa analítico. Los resultados obtenidos muestran la necesidad de repensar las disciplinas mediante la asignación de un mayor énfasis en el conocimiento epistemológico de la ciencia. La inclusión de los aspectos de la Historia y Filosofía de la Ciencia se puede considerar como un eje integrador clave para comprender los contenidos específicos de la materia que se enseña y es una de las posibles formas de mejorar la comprensión de la naturaleza de ciencia. Este estudio puede ayudar en las discusiones y experiencias curriculares de otras universidades, que incluyen la disciplina de Historia de la Ciencia y / o Química en sus currículos.

By using the Monte Carlo simulation platform with probabilistic mathematical functions of the Boltzmann type, <img src="/img/revistas/qn/v36n5/a20res.jpg" align="absmiddle"/>, having activation energy and temperature as parameters, it was possible to assess important dynamic aspects of homogeneous chemical reactions of the types A → B and A <img src="/img/revistas/qn/v36n5/20s01.jpg" align="absmiddle"/> B. The protocol proved a useful tool in work with the basic concepts of Kinetics and Thermodynamics allowing its application both in class activities and for assisting experimental procedures.

Bananas verdes [Nanicão (Musa sp., subgrupo Cavendish) e Prata (Musa sp., subgrupo Prata)] foram estudadas durante o seu amadurecimento. As propriedades físicas (firmeza), físico-químicas (pH, acidez total titulável e sólidos solúveis) e químicas (açúcares, compostos fenólicos e voláteis) foram analisadas e demonstraram diferenças significantes (p < 0,05) entre as bananas. A banana Prata apresentou valores mais altos de compostos fenólicos, sólidos solúveis, açúcares e firmeza do que a banana Nanicão. O método de coleta e análise dos compostos voláteis foram o headspace em dedo frio e a cromatografia gasosa. Os ésteres acetatos, butiratos, isobutiratos e isovaleratos foram predominantes. A banana Prata produziu maiores concentrações de voláteis do que a Nanicão, exceto para os acetatos. O comportamento das curvas de produção dos ésteres seguiu um aumento contínuo, até um pico, para em seguida apresentar uma diminuição no estágio de escurecimento das cascas dos frutos.

Fresh green bananas [Nanicão (Musa sp., subgroup Cavendish) and Prata (Musa sp., subgroup Prata)] were studied during their ripening. Physical (firmness), physicochemical (pH, total titrable acidity and soluble solids) and chemical properties (sugars, phenolics and volatile compounds) were analyzed and showed significant differences (p < 0.05). Prata presented higher values of phenolic compounds, soluble solids, sugars and firmness than Nanicão. A method to quantify the emission of esters was developed by cryogenic headspace and gas chromatography. Acetates, butyrates, isobutyrates and isovalerates were predominant. Prata produced a higher volatile concentration than Nanicão, except for acetates. In most cases, the amount of volatiles increased continuously until peel browning, followed by a decrease or a plateau.

Fresh green bananas (Musa sp., subgroup Prata) were treated with a dose of only 90 ηg g-1 of 1-MCP for 13 hours and the evolution of the volatile compounds along the ripeness was studied. A method to quantify the emission of esters was developed by cryogenic headspace and gas chromatography. Esters of acetate, butyrate, isobutyrate and isovalerate were found as major compounds. The application of the 1-MCP for 13 hours delayed the appearance of the coloration 8 of the peel for 3 days and decreased quantitatively in about 46% the total production of esters in the banana until the 15° day of harvested.