Page - 7 - in Advanced Chemical Kinetics

Theenergyrequiredtopass thereactantER toactivatedcomplexEΘ is calledactivationenergy or energyof activationEAct:EΘ–ER. Itmaybe supplied in any form,mechanical, chemical, or thermal, toenable the reactant toconvert into theproduct, i.e., XN i¼1 αSiAi↦ E F Act _ ↦ XN i¼1 βSiAi (6) Theactivation energyduring the forwardEFAct andbackwardE B Act reactionsmust be the same ordifferentdependingonthetypeof reactions. In thermos, theneutral reactionandΔH=0, the energy of activation in both the directions are same. While in endothermic reactions, EFAct>E B Act, holdsandinexothermicreactions,E F Act<E B Act. It isalsounderstoodthat thehigher theactivationenergy, theslower the reaction. The activated complex is a separate entity and there exists an equilibriumbetween reactants (products,underreversiblereactions)andactivatedcomplex(Figure1).Thus,areactionmech- anismcanbedefinedas XN i¼1 αSiAi<¼>Θi¼> XN i¼1 βSiAi (7) But still, there is someactivationgoingonbetweentheactivatedcomplexesΘ∓i , i.e., Θ∓i : Θ R i ¼>ΘPi : Therefore, a complete complex chemical reaction mechanism can be defined as PN i¼1 αSiAi⇔ Θ∓i ) PN i¼1 βSiAi. Figure1. Acomplexreactionmechanisminvolvingenergybarriersandtransitionstates. Complex Reactions and Dynamics http://dx.doi.org/10.5772/intechopen.70502 7