Rate constant

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The rate constant is used in reaction kinetics to show the proportionality of the reaction rate to the concentrations of the starting materials. It is indirectly a measure of the speed of a chemical reaction.

For an example reaction is the reaction rate

where is the rate constant of the reaction and the respective partial reaction order. The unit of the rate constant depends on the overall reaction order :

Occasionally, the rate equation is also with activities at: . Then the occurring rate constant has the unit and is not to be confused with the rate constant above.


The rate constant can be calculated using the empirical Arrhenius equation (or using transition state theory ):


The temperature dependence of the frequency factor is derived from the impact theory :


The frequency factor corresponds to the product of the collision number  Z and the orientation factor  P . The frequency factor thus indicates the maximum number of collisions in the gas phase, taking into account the orientation of the molecules necessary for the reaction.

See also

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