- Enthalpy of activation (∆H‡) and entropy of activation (∆S‡):
∆G° = ∆H° – ∆S° ⇒ ∆G‡ = ∆H‡ – ∆S‡
1) ∆H‡ is the difference in bond energies between the reactants and the transition
state.
i) It is the energy necessary to bring the reactants close together and to bring
about the partial breaking of bonds that must happen in the transition state.
ii) Some of this energy may be furnished by the bonds that are partially formed.
2) ∆S‡ is the difference in entropy between the reactants and the transition state.
i) Most reactions require the reactants to come together with a particular
orientation.
ii) This requirement for a particular orientation means that the transition state
must be more ordered than the reactants and that ∆S‡ will be negative.
iii) The more highly ordered the transition state,the more negative ∆S‡ will be.
iv) A three-dimensional plot of free energy versus the reaction coordinate:Figure 6.3 Mountain pass or col analogy for the transition state.