Asia-Pacific Forum on Science Learning and Teaching, Volume 9, Issue 1, Article 5 (Jun., 2008)
Fatma TÜRK and Muammer ÇALIK

Using different conceptual change methods embedded within 5E model: A sample teaching of Endothermic – Exothermic reactions

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Appendix B





雲朵形圖說文字: I wonder if an endothermic reaction can happen spontaneously.
Do the terms ‘endothermic’ and ‘exothermic’ have the same meaning?



Some of the students’ alternative conceptions are:

 Students are unable to comprehend and differentiate the relationship between exothermic and endothermic reactions

 Endothermic reactions take place spontaneously

 Students have difficulty discriminating the activation energy from the total enthalpy change of the reaction.

Some students think that any endothermic reaction may happen spontaneously. However, such an idea is not very common, except for three different endothermic reactions: (i) Dissolving ammonium salts in water (ii) Reaction of solid barium hydroxide with ammomium salts (iii) Reaction of solid ammonium carbonate with carboxylic acids (i.e. ethanoic acid, propanoic acid, butanoic acid). Therefore, the idea ‘endothermic reactions cannot occur spontaneously’ is generally accepted. To decide if a reaction is either endothermic or exothermic, we look at the total energy as a consequence of releasing energy in bond formation and absorbed energy in bond breaking. Similarly, the terms ‘endothermic’ and ‘exothermic’ do not have the same meaning because these terms reflect the type of reaction based on enthalpy change. Further, activation energy and total enthalpy energy are different from each other. That is, activation energy, also called threshold energy, is defined as the energy that must be overcome in order for a chemical reaction to take place. However, total enthalpy change is a result of chemical reactions.

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