Vyboishchi

Apuntes

Vyboishchikov (1) Cinètica Química i Dinàmica Molecular Chemical Kinetics and Reaction Dynamics Sergei Vyboishchikov Vyboishchikov (4) CHEMICAL KINETICS • Why chemical kinetics? Thermodynamics does not tell us how fast a reaction is. ► Phenomenological (“formal”) Chemical Kinetics studies reaction rates (= velocitats de reacció); Rate prediction using molecular data only is not possible (∆rH°, ∆rG° are of no help); Determination of reaction mechanism is possible in principle (not always in practice). ► Reaction dynamics (= dinàmica molecular) studies what exactly happens in an elementary process: changes in geometric configu- ration, energy redistribution etc. Intents to predict reaction rates for elementary reactions. Vyboishchikov (5) Reaction mechanism • Elementary reactions: ► Those in which the reactants transform into products directly: A + B → Product(s) • Most observed chemical reactions are complex (not elementary) ► A reaction is usually a succession of several elementary reactions (steps = etapes); ► A product of one of the steps that serves as reactant for a subse- quent step is referred to as intermediate. ► The mechanism is the succession of all the elementary steps l...