View source for Bell–Evans–Polanyi principle

In [[physical chemistry]], the '''Evans–Polanyi principle''' (also referred to as the '''Bell–Evans–Polanyi principle''', '''Brønsted–Evans–Polanyi principle''', or '''Evans–Polanyi–Semenov principle''') observes that the difference in [[activation energy]] between two reactions of the same family is proportional to the difference of their [[enthalpy of reaction]].

This relationship can be expressed as

: <math>E_\text{a} = E_0 + \alpha \Delta H,</math>

where

: <math>E_0</math> is the [[activation energy]] of a reference reaction of the same class,
: <math>\Delta H</math> is the [[enthalpy of reaction]],
: <math>\alpha</math> characterizes the position of the [[transition state]] along the [[reaction coordinate]] (such that <math>0 \leq \alpha \leq 1</math>).

The Evans–Polanyi model is a [[Free-energy relationship|linear energy relationship]] that serves as an efficient way to calculate [[activation energy]] of many reactions within a distinct family. The [[activation energy]] may be used to characterize the [[Reaction rate constant|kinetic rate parameter]] of a given reaction through application of the [[Arrhenius equation]].

The Evans–Polanyi model assumes that the [[pre-exponential factor]] of the [[Arrhenius equation]] and the position of the [[transition state]] along the [[reaction coordinate]] are the same for all reactions belonging to a particular reaction family.

==See also==
* [[Hammond's postulate]]
* [[Free-energy relationship]]
* [[Brønsted catalysis equation]]
* [[Catalytic resonance theory]]

==References==
* {{Cite book|title=Advanced Organic Chemistry (Part A: Structure and Mechanisms)|last=Carey|first=Francis, A.|date=2007|publisher=Springer|last2=Sundberg|first2=Richard, J.|isbn=978-0-387-44897-8|edition=5th|location=New York|oclc=154040953}}
* {{Cite book|title=Molecular Driving Forces: Statistical Thermodynamics in Biology, Chemistry, Physics, and Nanoscience|last1=Dill|first1= Ken A.|date=2011|publisher=Garland Science|last2=Bromberg|first2=Sarina|isbn=978-0-8153-4430-8|edition=2nd|location=London|oclc=660161826}}
* {{Cite journal|last=Vinu|first=R.|last2=Broadbelt|first2=Linda J.|author-link2=Linda Broadbelt|date=2012|title=Unraveling Reaction Pathways and Specifying Reaction Kinetics for Complex Systems|journal=Annual Review of Chemical and Biomolecular Engineering|language=en|volume=3|issue=1|pages=29–54|doi=10.1146/annurev-chembioeng-062011-081108|pmid=22468596|issn=1947-5438}}
==Notes==
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{{DEFAULTSORT:Bronsted-Evans-Polanyi Principle}}
[[Category:Enthalpy]]
[[Category:Thermochemistry]]