Chapter 9 Phenomenological chemical kinetics (empirical/classical) -- experimental aspects § 9.1 Introduction of chemical kinetics

Levine p reaction kinetics rate of reaction, rate laws, reaction mechanism 17.2 measurement of reaction rates 17.3 integration of rate law first-order reactions; second-order reactions; third-order reactions zero-order reaction; n-th-order reaction

1.1 details about a chemical reaction 1) Stoichiometric: balance of the equation 2) Thermodynamic: Spontaneity and equilibrium 3) Kinetic: Rate and mechanism The factor concerned by thermodynamics is the inherent tendency or the possibility and the advancement of the reaction but not the reality and the rate. is spontaneous. Fortunately, this reaction is too slow to be detectable.

Thermodynamics and kinetics concern different aspects of reaction, for example: Thermodynamics: reaction direction (spontaneity); maximum yield (equilibrium). Kinetics: rate (catalyst, temperature), mechanism

Chemical kinetics: a branch of chemistry that concerns reaction rate and mechanism. Main concerns of chemical kinetics: 1)Reaction rate: factors that determines the rate of reaction, rate law. 2) Reaction mechanism: the series of steps by which a reaction takes place. 3) structure-dependence of reactivity: the correlation between molecular structure and reaction potential.

1.2 reaction mechanism and elementary reaction H 2 + I 2 = 2 HI 1) I 2 = 2I 2) 2I + H 2 = 2HI H 2 + Br 2 = 2 HBr 1) Br 2 = 2 Br 2) Br + H 2 = HBr + H 3) H + Br 2 = HBr + Br 4) H + HBr = H 2 + Br 5) 2 Br = Br 2 the detailed way by which the reactants are converted into products, or the series of steps by which a reaction takes place. Reaction mechanism / reaction pathway multistep reaction

The reaction that completes in one act is called elementary reaction. The sum of the elementary reactions and their series is called the mechanism of the overall reaction. 1) Br 2 = 2Br 2) Br + H 2 = HBr + H 3) H + Br 2 = HBr + Br 4) H + HBr = H 2 + Br 5) 2 Br = Br 2 The species such as H and Br formed in one step and consumed in a subsequent step and never seen as a product is called an intermediate.

1.3 Classification of reactions 1) elementary reactions According to the number of molecules involved in the reaction, elementary reactions can be divided into three kinds: unimolecular reaction: (decomposition, isomerization) I 2 = 2I bimolecular reaction: (combination) Br + H 2 = HBr + H termolecular reaction: 2I + H 2 = 2HI The probability of three-molecule colliding simultaneously is very small, termolecular reaction are quite rare. The elementary reaction with four reactant molecules in gaseous phase has not been found.

According to the number of elementary reactions involved, the overall reaction can be classified into: 2) overall reactions Ethylene butadiene cyclohexene Find differences between mechanisms described in physical chemistry and those shown in organic chemistry. simple reaction Diels-Alder addition: complex reaction Overall reaction

Hydrolysis of nitrile