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5.6: Activated Complex

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    Activated Complex

    Reactant particles sometimes collide with one another and remain unchanged by the collision. Other times, the collision leads to the formation of products. The state of the particles that is in between the reactants and products is called the activated complex. An activated complex is an unstable arrangement of atoms that exists momentarily at the peak of the activation energy barrier. Because of its high energy, the activated complex exists for an extremely short period of time (about \(10^{-13} \: \text{s}\)).

    Activated complex.png

    Figure \(\PageIndex{1}\): The activated complex exists momentarily at the peak of the activation energy barrier.


    There is an equal likelihood that the activated complex either reforms the original reactants or goes on to form products. The figure below shows the formation of a possible activated complex between colliding hydrogen and oxygen molecules to form water. Because of their unstable nature and brief existence, very little is known about the exact structures of many activated complexes.

    CK12 Screenshot 18-5-1.png
    Figure \(\PageIndex{2}\): An activated complex is a short-lived state in which the colliding particles are at the peak of the potential energy curve. (CC BY-NC; CK-12)


    • The role of the activated complex in reactions is described.

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    5.6: Activated Complex is shared under a CC BY-NC license and was authored, remixed, and/or curated by LibreTexts.

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