Essay: Alternative conceptions of chemical equilibrium

Here’s my second essay in teacher training at Monash University.🙂

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Students lacking an understanding of chemistry are at a disadvantage when applying for jobs in many lucrative industries (including natural resources such as coal, oil and gas; drug production; biotechnology; chemical production; and modern agriculture). Lack of understanding of chemistry can also endanger a student’s health because many household chemicals are hazardous when misused or mixed (Consumer and Environmental Health Services, 2010).

One of the most commonly confused concepts in chemitsry is that of chemical equilibria (Şendur, 2011). A chemical equilibrium occurs when “the rates of the forward and reverse reactions are equal” (Bickmore, 2013). Chemical equilibria are introduced at Year 12 in Victorian secondary schools as part of the Australian science curriculum (Victorian Curriculum and Assessment Authority, 2013). However, many students complete their secondary schooling with an incorrect understanding of chemical equilibria, which limits students’ career prospects and their options for further study (Camacho & Good, 1989).

Wenning (2008) writes that, “students come to school with non-traditional ideas that deal with the natural world that are highly resistant to change and strongly influence new learning”. Kousathana & Tsaparlis (2002) support this theory and suggest that “alternative conceptions” (ACs) are the main cause of misunderstanding. Rather than being “empty vessels” who know little or nothing about a topic, students in fact come to class with a range of ACs, many of which are wrong (Drori, 2007). Students construct ACs from conversations, from the media, from misinterpretation of personal experience, or even from a misinterpretation of the material taught in school. Once ACs are constructed, they are “tenacious and resistant to extinction by conventional teaching strategies” (Chiappetta & Koballa Jr., 2006). When ACs contradict the material being taught, it is imperative that teachers address students’ pre-existing views before introducing new curriculum content, or the new content will be rejected completely (Şendur, 2011). Only this “investigate and disprove ACs” approach allows students to develop a ‘correct’ interpretation of the material being taught.

This paper discusses three common ACs that students hold relating to chemical equilibria (from Hackling & Garnett, 1985) and suggests teaching techniques that educators can use to overcome each one.

First, there is a commonly held AC that catalysts affect only the forward or the reverse reaction, but not both (Garnett et al., 1995). By logical extension, this AC leads to the misconception that adding a catalyst to a system in dynamic equilibrium can alter the ratio of reactant to product (Hackling & Garnett, 1986). This AC is in direct conflict with our current scientific understanding, which is that catalysts increase both the forward and the reverse reaction rates equally, leaving the ratio of reactants to products unchanged (Nyman & Hamm, 1968). The AC could arise from students’ knowledge of catalysts found in daily life (e.g. catalytic converters found in cars), which tend to catalyse reactions whose initial states are far from equilibrium, giving the impression that only the forward reaction rate is being increased. However, catalysts do allow systems to reach equilibrium faster. Teachers need to address this AC both mathematically and through practical demonstration to avoid confusion.

Second, some students held the AC that reaction rates increase after a reaction has started (Garnett et al., 1995). The accepted scientific view is that reactants in aqueous solution react with a high initial reaction rate, which then decreases exponentially as the concentration of reactant also decreases (Nyman & Hamm, 1968). This AC could have formed from students’ years of experience with lighting fires, dissolving effervescent tablets, or cooking certain foods (e.g. nuts, seeds or popcorn, which remain unchanged in a hot pan for several minutes before cooking suddenly). These observations give the impression that chemical reactions take time to “get going” (Hackling & Garnett, 1986). An experiment as simple as sequentially brewing tea in water, then analysing the colour of the resulting liquors can illustrate to students that initial reaction rates are almost always the highest (due to high concentration of reactants), and these rates almost never increase over time.

Finally, a number of students hold the AC that all equilibria are static, immobile end-points at which the molecules are no longer reacting (Garnett et al., 1995). The standard scientific view that dynamic equilibrium is an active process in which the forward and reverse reactions occur at equal rates (Nyman & Hamm, 1968) can be difficult for students to grasp due to the lack of visual evidence. Upon visual observation, systems appear not to change once equilibrium has been reached. Teachers can help students understand the concept of dynamic equilibrium by discussing “what would happen if I added more of [reactant X]?” and “what would happen if we siphoned away [product Y]?” with students.

Alternative conceptions left unresolved by inadequate secondary-level teaching practices could have wide-ranging, long-term negative effects on students’ lives. If students do not learn to overcome their alternative conceptions at secondary level, university concepts will be harder to understand, and life-long learning—a key goal of schooling—would be hindered greatly. To quote Layton (1991), it is only when student “deconstruct and reconstruct” alternative conceptions that life-long learning becomes possible. ■

842 words

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References

Bickmore, B. (2012). Chemical Equilibrium Misconceptions. Retrieved from http://serc.carleton.edu/sp/library/mathstatmodels/examples/35770.html

Camacho, M. & Good, R. (1989). Problem solving and chemical equilibrium: Successful versus unsuccessful performance. Journal of Research in Science Teaching, 26, 251-272.

Chiappetta, E. L. & Koballa Jr., T. R. (2006). Science Instruction in the Middle and Secondary Schools. Developing Fundamental Knowledge and Skills for Teaching; 6th ed., Columbus, OH: Pearson Merrill Prentice Hall.

Consumer and Environmental Health Services (CEHS) (2010). Common Cleaning Products May Be Dangerous When Mixed. Retrieved from http://www.state.nj.us/health/eoh/cehsweb/bleach_fs.pdf (17/03/2013)

Garnett, P.J., Garnett, P.J. & Hackling, M.W. (1995): Students’ Alternative Conceptions in Chemistry: A Review of Research and Implications for Teaching and Learning, Studies in Science Education, 25:1, 69-96

Hackling, M.W. & Garnett, P.J. (1985). Misconceptions of chemical equilibrium. European Journal of Science Education, 7, 205-214.

Hackling, M.W. & Garnett, P.J. (1986). Chemical equilibrium: Learning difficulties and teaching strategies. Australian Science Teachers Journal, 31, 8-13.

Kousathana, M. & Tsaparlis, G. (2002). Students’ Errors In Solving Numerical Chemical-Equilibrium Problems. Chemistry Education: Research and Practice in Europe, 3, 5-17.

Layton, D. (1991). Science education and praxis: the relationship of school science to practical action. Studies in Science Education, 19, 43-79.

Nyman, C. J. & Hamm, R. E. (1968). Chemical equilibrium, Boston, Mass.: Raytheon Education Co.

Şendur, G. et al. (2011). How Can Secondary School Students Perceive Chemical Equilibrium? E-Journal of New World Sciences Academy, 6, article 1C0388. Retrieved from http://www.academia.edu/882873/How_Can_Secondary_School_Students_Perceive_Chemical_Equilibrium (17/03/2013)

Victorian Curriculum and Assessment Authority. (2013). AusVELS and the Australian Curriculum. Retrieved from http://ausvels.vcaa.vic.edu.au/Print (15/03/2013)

Wenning, C. J. (2008). Dealing more effectively with alternative conceptions in science. Journal of Physical Teacher Education Online, 5(1), Summer 2008, pp. 11-19.

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