Reflections catalyzed by an assault on a favorite principle

摘要

This commentary disagrees with a recent submission (Cheung, D. J. Chem. Educ. 2009, 86, 514-518) questioning the value of the Le Ch telier principle (LCP). Cheung points out that the LCP fails to predict the proper change in a small set of chemical equilibria. This commentary argues that the LCP has great qualitative utility in correctly predicting perturbations in most common chemical phenomena. Cheung argues for abandoning the LCP in high school teaching based on a limited number of misfirings of the LCP not congruent with mathematical equilibrium calculations. The commentary takes off from this suggestion to ask: (i) What expectations should we have for secondary teachers of chemistry? (ii) What should be the balance and harmony of qualitative and quantitative components in secondary chemistry? (iii) How should we deal with exceptions to rules or principles? The commentary concludes in arguing for a proper balance of qualitative and quantitative teaching of chemistry and coupling that teaching to explaining real problems that have a significant chemical dimension (global warming). The author believes that this approach would result in higher visibility and greater respect for chemistry.