Appendix B
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.
Copyright (C)
2008
HKIEd
APFSLT. Volume
9,
Issue
1,
Article 5 (Jun.,
2008).
All Rights Reserved.
