Bell–Evans–Polanyi principle
The Bell -Evans - Polanyi principle is a model that establishes a relationship between the activation energy and the enthalpy of reaction of a chemical reaction. It states that is given in a series of similar reactions, a linear relationship between the above reaction constants. The activation energy is therefore the lower the lower the enthalpy of reaction. The basic principles were described in the 1930s in publications by RP Bell and MG Evans and M. Polanyi.
The Bell -Evans - Polanyi principle allows both thermodynamic and kinetic statements about a series of chemical reactions to formulate:
The general derivation of the Bell -Evans -Polanyi principle is the Hammond postulate.
A good example of the Bell -Evans -Polanyi principle is the pyrolysis of azo compounds. This azo compound is released from the set of molecular nitrogen, the radicals of the corresponding organic radicals are formed. The reaction enthalpy? HR functions depends on the energy content of the reactants and the stabilization of the radicals formed. The activation energies ΔHA behave relatively However, as the reaction enthalpies ( see figure).