Análise do princípio de Le Chatelier em livros didáticos de química

Abstract

CANZIAN, R., Le Chatelier’s Principle Analysis in chemical textbooks. 2011. 80 f. Dissertacao (Mestrado). Instituto de Quimica, Instituto de Fisica, Instituto de Biociencias e Faculdade de Educacao, Universidade de Sao Paulo, Sao Paulo, 2011. This work presents a reflection on the role of the Le Chatelier‟s principle concerned by its creation and some implications in the teaching of chemistry. The main purpose was to analyze as high school chemical textbooks approach with this subject. For this, historical aspects of the evolution of the principle were studied with the objective of discussing important characteristics, for example: the universal character of the principle, his problems and limitations regarding their applications to previse changes in chemical equilibrium systems and the possible alternatives to the use of the principle. It was found that the principle formulations were similar to that more simple and popular wrote by Le Chatelier, in the year of 1888. It was also made an analysis of how the textbooks address the issue of variables that influence in the state of equilibrium such as: concentration, pressure, catalyst and temperature. Also was analyzed the i llustrations present in these books with the objective of address the equilibrium change based in the of Johnstone‟s triangle (that explicitly shows the macroscopic, microscopic and representational levels of chemical knowledge). The main results showed that the majority of the figures in textbooks refers only to macroscopic level and the effects done by of the equilibrium reactants concentration change. There are few figures which are related the three levels represented in the Johnstone‟s triangle. Is very important that teachers include the illustrations missing, mainly the microscopic level, once that this level is essential to correct understand of chemical equilibrium change in the molecular level. In general, the authors of chemical textbooks present the Le Chatelier‟s principle in an inductive manner, vague and ambiguous. They never present theoretical aspects and limitations in the application of the principle. This stresses the infallible character of Le Chatelier‟s principle and transmits the idea that it is an absolute truth. This superficial treatment of the principle can encourage processes of teaching-learning based on memorization and the students can correctly use the principle in the problems solutions without have an exact understanding the phenomena.