Gibbs free energy of activation

Finally, exchange is a kinetic process and governed by absolute rate theory. Therefore, study of the rate as a fiinction of temperature can provide thennodynamic data on the transition state, according to equation (B2.4.1)). This equation, in which Ids Boltzmaim s constant and h is Planck s constant, relates tlie observed rate to the Gibbs free energy of activation, AG. ... 

Fig. 16. A. Plot of log iNa as a function of T 1 (°K) using the experimental values of the rate constants and the location of the binding sites in Eq. 4. The Gibbs free energy of activation is calculated from Eq. 3 the AS are taken to be zero, and the current is calculated by means of Eq. 4. The purpose is to demonstrate that multibarrier channel transport can be seen as single rate process with average values for the enthalpies of activation. Non-linearity of such a plot is then taken to arise form the dynamic nature of the channel.

Transition state theory gives the Gibbs free energy of activation from either of the forms as... 

We shall reformulate Eq. (7-54) on thermodynamic grounds, introducing A//, AS, and AG, the standard Gibbs free energy of activation. These expressions also follow from Eq. (7-37). 

These techniques are known as linear free energy relations, LFER. Imagine that one has determined the rate constants, or the Gibbs free energies of activation, for a series of reactions. The reactions are all the same, save for (for example) a different substituent on each reactant. The substituent is not a direct participant in the reaction. In an LFER, the values of log k or AG are correlated with some characteristic of the substituent as manifested in another reaction series. If the correlation is successful, then the two series of reactions have a common denominator. This technique has proved to be a powerful one for systematizing reactivity. We shall see a number of such correlations. 

Gibbs (free) energy of activation (AG ), 10, 84, 165 heat capacity of activation (ACP ), 160-161... 

According to Marcus theory [69-71], in the absence of work terms, the Gibbs free energy of activation for an ET reaction is given by ... 

Given that the overpotential alters the Gibbs free energy of activation, it should be expected that the net current density increases exponentially with overpotential. This dependence was observed by Tafel, who developed the relationship bearing his name.26... 

The standard enthalpy difference between reactant(s) of a reaction and the activated complex in the transition state at the same temperature and pressure. It is symbolized by AH and is equal to (E - RT), where E is the energy of activation, R is the molar gas constant, and T is the absolute temperature (provided that all non-first-order rate constants are expressed in temperature-independent concentration units, such as molarity, and are measured at a fixed temperature and pressure). Formally, this quantity is the enthalpy of activation at constant pressure. See Transition-State Theory (Thermodynamics) Transition-State Theory Gibbs Free Energy of Activation Entropy of Activation Volume of Activation... 

Pi)Ay /Rr. Thus, In 2 = (3000 - l)Ay /(82.05 X 298) = 5.7 cm. This exercise indicates that reaction rate is relatively insensitive to pressure changes if Ay is small. See Transition-State Theory Expressed in Thermodynamic Terms Gibbs Free Energy of Activation Enthalpy of Activation Entropy of Activation lUPAC (1979) Pure Appl. Chem. 51, 1725. 

TRANSITION-STATE THEORY GIBBS FREE ENERGY OF ACTIVATION ENTROPY OF ACTIVATION VOLUME OF ACTIVATION ENTROPY... 

E Initial kinetic energy of relative motion of reactants Electric vector of light A G° per mole Standard Gibbs free energy of activation... 

The Gibbs free energy of activation, AG, may be separated into enthalpic and entropic terms, if required, by using another relationship from equilibrium thermodynamics,... 

AG Gibbs free energy of activation HIV human immunodeficiency virus... 

Modern theoretical developments in the theory of proton-transfer reactions suggest that such linear Bronsted plots are only a first approximation when the range of the P-KHA-values is narrow. When a wider range of bases is used, the curve obtained should be such that the Gibbs free energy of activation AG fits the Marcus eqn (6). This equation was derived (Cohen and Marcus, 1968 ... 

Typically, the Gibbs free energy of activation of most chemical reactions consists of a large internal energy of activation AE, along with much smaller contributions from pressure-volume effects P AV or from the entropy AS ... 

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