The Adverse Effects of Le Châtelier's Principle on Teacher Understanding of Chemical Equilibrium

Abstract

Chemistry education researchers have noted the inadequacy of Le Châtelier's principle (LCP) for decades (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). They have shown how apparently reasonable applications of LCP can result in incorrect predictions about the effects of changes in concentration, volume, pressure, or temperature on chemical systems at equilibrium. Because LCP has no value for chemistry teachers and students other than historical interest, some researchers (13-19) have criticized the over-emphasis of LCP in the school chemistry curriculum. They have recommended the use of the equilibrium law, reaction quotient, and van't Hoff equation to predict the direction in which a chemical equilibrium system will shift when it is disturbed. Yet little progress has been made to delete LCP from the school chemistry curriculum. Textbooks of high school chemistry or college chemistry published in many countries such as the United States, the United Kingdom, Australia, Canada, and China still rely on LCP as the major predictive tool. Le Châtelier himself described three different statements of LCP (18). Petrucci, Harwood, and Herring (20) emphasized that it is hard to state LCP unambiguously, but they believed that the essential meaning of LCP is as follows: When an equilibrium system is subjected to a change in temperature, pressure, or concentration of a reacting species, the system responds by attaining a new equilibrium that partially offsets the impact of change (20, p 641; emphasis in original).

A mathematical approach to chemical equilibrium theory for gaseous systems IV: a mathematical clarification of Le Chatelier’s principle

“…By the analysis given above, it can be concluded that Le Chatelier's principle cannot be applied in the example represented by Eq. 1, since the concentrations for both N 2 and H 2 are affected by the addition [5]. When 1 mole of N 2 is added x N 2 is increased by 0.5-0.6973 from rows No.…”

“…It is more useful to obtain a general understanding with theoretical analysis. A simple analysis [5] shows that the addition of N 2 at constant T and P will produce more N 2 because of the dilution of H 2 resulting from the addition. But it will be clear that this explanation does not help much in developing a more systematic mathematical method [15][16][17].…”

“…However thermodynamics itself does not automatically provide enough mathematical tools for the analysis of complicated systems. Several negative effects associated with Le Chatelier's principle [5,6] have been identified [7][8][9][10][11][12]. The inclusion of Le Chatelier's principle causes problems because it can be, and often is, used in situations for which it is not applicable, especially with gaseous systems at constant temperature T and pressure P. Unfortunately it is difficult to predict when the principle is not applicable.…”

“…The inclusion of Le Chatelier's principle causes problems because it can be, and often is, used in situations for which it is not applicable, especially with gaseous systems at constant temperature T and pressure P. Unfortunately it is difficult to predict when the principle is not applicable. Cheung [5] concluded from these negative effects that Le Chatelier's principle was vague and has no value for chemistry other than historical interest. Although we agree with this view to some extent, it is relevant to say that the principle retains relevance but must be used correctly.…”

Conceitos alternativos sobre equilíbrio químico e suas consequências no aprendizado de bioquímica: diagnóstico e intervenções recuperatórias

“…Os dados mostram uma grande quantidade de conceitos alternativos provenientes do ensino médio (Akkus et al, 2003), cuja origem pode ser atribuída, pelo menos em parte, aos próprios professores que carregam consigo conceitos alternativos sobre equilíbrio químico ) e sua natureza fenomenológica -notavelmente uma associação inconsistente com o princípio de Le Chatelier (Cheung, 2009). Além disso, há dados sobre os conceitos alternativos em EQ dentro do enfoque dos diferentes níveis de representação (Carobin, Serrano, 2007), que será abordado adiante.…”