Endo, Exothermic Reactions and Energy
Name: Emily M.
Date: Sunday, December 08, 2002
What is the difference between an endo and exothermic
reaction. What are some examples? Like where does the energy for each
come from? I am told the energy is in the chemical bonds, but I am also
told that a bond is at low potential. It cannot be at high and low
energy at the same time. Please help!
Net endo-energetic reactions require energy to proceed. Net exo-energetic
reactions release energy as they proceed.
If bonds are to be broken, activation energy must be supplied. When new
bonds are formed, energy is released.
Overall, the energy to drive chemical reactions is either input as
activation energy at the start or it comes from energy released as atoms
rearrange into other kinds of ions or molecules.
Endothermic reactions absorb heat. Exothermic give off heat. Dilution of
ammonium chloride is an example of an endothermic reaction. This is the
active ingredient in chemical "ice packs" you can obtain in a pharmacy.
Other "reactions" are melting and boiling which also absorb heat to happen,
although you may not consider them "chemical" reactions. Combustion is a
typical exothermic reaction -- any type of burning.
An exothermic reaction occurs if the energy of the bonds formed in the
products are stronger (lower energy) than the bonds broken in the reactants.
Endothermic reactions require heat. If there is no external source, the
reaction "gets" the heat by cooling to a lower temperature. These reactions
are driven by the change in the configuration of the atoms. If the atoms in
the product molecules have a less orderly structure than the atoms in the
reactants, these reactions will occur even if the "cost" some energy to
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Update: June 2012