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Name |
Arrhenius Rate Equation |
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Equation |
k
=
A
exp
(
-
E
a
/
R
T
)
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Definition of terms |
k = rate of reaction, A = frequency factor, E a = activation energy, R = gas constant, T = temperature |
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Comments |
The Arrhenius rate equation describes the rate of chemical reactions.
It is based on the assumption that a molecule needs to have a certain amount of energy, known as the activation energy, to cause a reaction. From the Boltzmann distribution the number of molecules with this or greater energy is equal to exp(−Ea/RT).
The pre-exponential factor A takes into account the number of molecules that are favourably orientated to cause the reaction. Although this frequency factor has a slight temperature dependence, over a small range, it is completely dwarfed by the temperature dependence of the exponential term.
If a reaction is carried out at different temperatures, and the rate constant measured at each, then a plot of ln k against -1/T could be made, the gradient of which would be Ea/R.
The Arrhenius rate equation and the concept of activation energy were developed by the Swedish chemist Svante Arrhenius (1859 - 1927). |
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References
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Chemistry: The central science , T L Brown et al ., Prentice Hall, 9th edition, 2002 |
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