Chemical equilibrium misconceptions

Ozkaya (76) studied conceptual difficulties experienced by prospective teachers in a number of electrochemical concepts, namely half-cell potential, cell potential, and chemical and electrochemical equilibrium in galvanic cells. The study identified common misconceptions among student teachers from different countries and different levels of electrochemistry. Misconceptions were also identified in relation to chemical equilibrium, electrochemical equilibrium, and the instrumental requirements for die measurement of cell potentials. Learning difficulties were attributed mainly to failure of students to acquire adequate conceptual understanding, and the insufficient explanation of the relevant... 

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

Chemical Equilibrium. The exchange of matter and energy is basically possible in two directions at the same time, in forward and backward reactions. As a result, there exists under certain constant conditions a defined relationship between reactants and products which one describes as chemical equilibrium [15]. In Chap. 6 misconceptions according to equilibria are reflected, teachinglearning suggestions are offered for every basic concept. 

Unfortunately, it seems to be difficult to teach this topic. Finley, Stewart and Yarroch [2] studied the level of difficulty of various themes in chemistry and reported the results of 100 randomly chosen teachers of chemistry from Wisconsin who chose chemical equilibrium as being clearly the most difficult theme overall. Berquist and Heikkinen [1] noted in addition Equilibrium, considered one of the more difficult chemical concepts to teach, involves a high level of students misunderstanding . One can therefore expect a large variety of misconceptions because of the difficulties in teaching this subject as well as for understanding it. 

Berquist and Heikkinen [1] have summarized students misconceptions concerning chemical equilibrium in many areas as follows ... 

Kousatana and Tsaparlis [6] present another summary of misconceptions of various sub-themes regarding chemical equilibrium. 

In 1992-1994, Kienast [7] carried out tests on chemical equilibrium with over 12,000 students in four test cycles. The following misconceptions, which were also described by the above-mentioned authors, were observed with particular regularity In equilibrium the sum of the amount of matter (concentration) of reactants is equal to the sum of the amount of matter (concentration) of the products (...) in equilibrium the amounts (concentrations) of all substances which are involved in equilibrium are the same (...) the sum of the amounts of matter (concentrations) remain the same during a reaction (...) data which has been supplied on the amount of matter (concentration data) should be multiplied with stoichiometric coefficients from the reaction equation, in order to find the true amount of matter concentration [7]. 

Because misconceptions about chemical equilibrium have been related in literature to student s lack of comprehension in basics of mathematics, they were also asked for their last grade in that subject. This way it was possible to gain an idea of whether there are correlations between students misconceptions relating to chemical equilibrium and the quality of their grades in mathematics. 

The answers and explanations contain misconceptions as already discussed. The following problems convey a connection to chemical equilibrium and -without giving any choice of answers - students were requested to supply answers, if possible detailed explanations. 

It is not simply and convincingly possible to counter the cited common misconceptions, i.e. that chemical equilibrium show equal concentrations of reactants and products . As an introduction, it might be helpful to show melting equilibria with different ice-water mixtures, or solubility equilibria with different amounts of the solid. 

Problem A widely accepted misconception on chemical equilibrium assumes that the concentration of reactants and products are equal. Attempts are made to demonstrate with different mixtures of varying ice and water portions, that at melting equilibrium, arbitrary amounts of water and ice can exist, that melting temperature of 0°C is always measured at normal conditions. If ice water mixtures are heated, the energy is taken to separate water molecules from the ice lattice, not to increase temperatures 0°C stays constant. 

Banerjee, A. Misconceptions of students and teachers in chemical equilibrium. International Journal of Science Education 12 (1991), 355... 

Wheeler, A.E., Kass, H. Student misconceptions in chemical equilibrium. Science Education... 

Misconceptions Associated with the Introduction of the Idea of Chemical Equilibrium... 

Many studies have documented students conceptual difficulties in the area of chemical equilibrium (e.g., Gussarksy Gorodetsky, 1990 Hackling Garnett, 1985 Maskill Cachapuz, 1989 Wheeler Kass, 1978 Johnstone, MacDonald Webb, 1977). Most of these studies concern students in upper secondary educabon. Some studies, however, have focused on university students of chemistry in the context of thermodynamic courses (e.g., Thomas Schwenz, 1998), or on chemistry teachers (Banerjee, 1991). Remarkably similar misconceptions were found across groups of students at different levels and from various countries. In particular ... 

Huddle, P.A. Pillay, A.E. (1996). An in-depth study of misconceptions in stoichiometry and chemical equilibrium at a South African university. Journal of Research in Science Teaching, 33, 65-78. 

Thinking it Through When a reaction has reached equilibrium, it does not mean that all chemical activity has stopped. Rather, at equilibrium, the macroscopic view indicates constant (but seldom equal) concentrations for each substance, making Choice (D) the correct response. Choice (A) is a commonly held misconception, one that you will not choose if you remember the concept of dynamic equilibrium. It is also untrue that the total moles of products must equal the remaining moles of reactant, choice (B). The relative amounts of material present at equilibrium will depend greatly on the position of the equilibrium, revealed in quantitative problems by the value of the equilibrium constant. Choice (C) is based on another common misconception about equilibrium reactions. Addition of a catalyst, while it may increase the rate at which equilibrium is achieved, does not affect the position of equilibrium. 

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