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 Reaction energies |
The general rule, then, is that when chemical
bonds form energy is released. The opposite case is much easier
to imagine: when chemical bonds are broken, energy must be
supplied or absorbed.
Since both bond-breaking and bond-making
generally occur in all but the simplest reactions it is the net
of these two energy changes which determines whether a reaction
liberates or absorbs energy. Both the formation of sodium
chloride and of water liberate heat. Such reactions are called
exothermic. Other reactions in which energy is absorbed are
called endothermic. |
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