Preferred Label : transition state theory;
IUPAC definition : A theory of the rates of elementary reactions which assumes a special type of equilibrium,
having an equilibrium constant K‡, to exist between reactants and activated complexes.
According to this theory the rate constant is given by: \[k \frac{k_{{B}}\ T}{h}\
K {\ddagger }\] where kB is the Boltzmann constant and h is the Planck constant. The
rate constant can also be expressed as: \[k \frac{k_{{B}}\ T}{h}\ \exp (\frac{Δ {\ddagger
}S {\,\unicode{x26ac}}}{R})\ \exp (- \frac{Δ {\ddagger }H {\,\unicode{x26ac}}}{R\
T})\] where Δ‡S , the entropy of activation, is the standard molar change of entropy
when the activated complex is formed from reactants and Δ‡H , the enthalpy of activation,
is the corresponding standard molar change of enthalpy. The quantities Ea (the energy
of activation) and Δ‡H are not quite the same, the relationship between them depending
on the type of reaction. Also: \[k \frac{k_{{B}}\ T}{h}\ \exp (- \frac{Δ {\ddagger
}G {\,\unicode{x26ac}}}{R\ T})\] where Δ‡G , known as the Gibbs energy of activation,
is the standard molar Gibbs energy change for the conversion of reactants into activated
complex. A plot of standard molar Gibbs energy against a reaction coordinate is known
as a Gibbs-energy profile; such plots, unlike potential-energy profiles, are temperature-dependent.
In principle the equations above must be multiplied by a transmission coefficient,
κ, which is the probability that an activated complex forms a particular set of products
rather than reverting to reactants or forming alternative products. It is to be emphasized
that Δ‡S , Δ‡H and Δ‡G occurring in the former three equations are not ordinary
thermodynamic quantities, since one degree of freedom in the activated complex is
ignored. Transition-state theory has also been known as absolute rate theory, and
as activated-complex theory, but these terms are no longer recommended.;
Origin ID : T06470;
See also
A theory of the rates of elementary reactions which assumes a special type of equilibrium,
having an equilibrium constant K‡, to exist between reactants and activated complexes.
According to this theory the rate constant is given by: \[k \frac{k_{{B}}\ T}{h}\
K {\ddagger }\] where kB is the Boltzmann constant and h is the Planck constant. The
rate constant can also be expressed as: \[k \frac{k_{{B}}\ T}{h}\ \exp (\frac{Δ {\ddagger
}S {\,\unicode{x26ac}}}{R})\ \exp (- \frac{Δ {\ddagger }H {\,\unicode{x26ac}}}{R\
T})\] where Δ‡S , the entropy of activation, is the standard molar change of entropy
when the activated complex is formed from reactants and Δ‡H , the enthalpy of activation,
is the corresponding standard molar change of enthalpy. The quantities Ea (the energy
of activation) and Δ‡H are not quite the same, the relationship between them depending
on the type of reaction. Also: \[k \frac{k_{{B}}\ T}{h}\ \exp (- \frac{Δ {\ddagger
}G {\,\unicode{x26ac}}}{R\ T})\] where Δ‡G , known as the Gibbs energy of activation,
is the standard molar Gibbs energy change for the conversion of reactants into activated
complex. A plot of standard molar Gibbs energy against a reaction coordinate is known
as a Gibbs-energy profile; such plots, unlike potential-energy profiles, are temperature-dependent.
In principle the equations above must be multiplied by a transmission coefficient,
κ, which is the probability that an activated complex forms a particular set of products
rather than reverting to reactants or forming alternative products. It is to be emphasized
that Δ‡S , Δ‡H and Δ‡G occurring in the former three equations are not ordinary
thermodynamic quantities, since one degree of freedom in the activated complex is
ignored. Transition-state theory has also been known as absolute rate theory, and
as activated-complex theory, but these terms are no longer recommended.
