Collision Model – Terminology


Effective Collision: a collision between particles that leads to bond breaking and bond forming.


Proper orientation: for a collision to be effective, the colliding particles must be oriented in such a manner that the proper parts of the molecules collide.

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Sufficient Energy: colliding particles must possess an amount of kinetic energy that surpasses the activation energy for the reaction.


Activated Complex: the short-lived intermediate structure that exists at the maximum energy location along the reaction pathway.

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Reaction Mechanism: the collection of steps by which reactants turn to products, forming several intermediate and short-lived species


Rate-Determining Step: the slowest step of a reaction mechanism. Not all steps of a mechanism occur at the same rate. The slowest step determines the overall rate of the reaction.


Important Note: For non-rate-determining steps, the concentration of reactants and products can be related by the equation:

[Reactants] = k • [Products] where k is a proportionality constant


Catalyst: a chemical that speeds up the rate of a reaction. The catalyst often alters the mechanism so that the activation energy is lowered.

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Role of Temperature: an increase in temperature increases the rate. At higher temperatures, there are a greater number of particles with a kinetic energy that surpasses the activation energy.

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Role of Concentration: an increase in concentration increases the rate because more collisions can occur in more regions of space where particles are more concentrated.

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Role of Surface Area: an increase in surface area increases the rate because there are more particles in the sample that are "freed up" and available for collisions.

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