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Bond Making & Breaking Tutorial

The for reactions in terms of Bond Energies (bond dissociation enthalpies)...

This segment of EXBAN presents a brief review of the for reactions in terms of bond breaking and making events. This is done to emphasize the large energies required to break bonds in comparison with overall values for reactions that can be negative or positive depending on the energy balance of the bonds ruptured and formed. Two factors that must be kept in mind:

(a) In the present depiction bonds are “pulled apart” and the fragments “snap” together to form new bonds in “tinker-toy” fashion. The overall for reactions can always be represented in this way, or in terms of the balance of bond breaking and making events employing appropriate bond dissociation enthalpies. The path the reaction actually takes for the transition between reactants and products will, of course, be quite different, and depend on the mechanism, e.g. whether the reaction is uncatalyzed, or catalyzed, etc.

(b) The misconception considered in this website is connected with the energy associated with bond breaking. The reactions here, including the coupled reaction, are examined, therefore, in terms of the ’s of the processes involved. Entropic contributions often contribute to the spontaneity of reactions, and can become the principal driving force for reactions or phase changes. It is, indeed, entropy that is responsible for the concentration dependence of reactions. However, bond breaking and making, as with the examples given here, is often the main factor in determining the spontaneity of reactions.

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