Lecture13 - Kinetics: Rates and Mechanisms of Chemical...

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1 Chapter 16 Kinetics: Rates and Mechanisms of Chemical Reactions Kinetics: Rates and Mechanisms of Chemical Reactions 16.1 Factors That Influence Reaction Rates 16.2 Expressing the Reaction Rate 16.3 The Rate Law and Its Components 16.4 Integrated Rate Laws: Concentration Changes over Time 16.7 Reaction Mechanisms: Steps in the Overall Reaction 16.8 Catalysis: Speeding Up a Chemical Reaction 16.5 The Effect of Temperature on Reaction Rate 16.6 Explaining the Effects of Concentration and Temperature Reaction Kinetics: Basic Concepts Need to know if reaction will occur or not (spontaneous) Æ Δ G Need to know how fast a reaction will occur Æ kinetics Factors that affect reaction rates: Collision frequency (concentrations of reactants) Orientation factors (must have correct alignment) Energy of collision must be sufficient to overcome energy barriers to reaction (e.g. bond breaking) Kinetics provide microscopic information on how reactions occur reaction mechanisms = control Review of Previous Lecture O 3 hole….saga of Science and kinetics done right Free Energy only tells if a reaction will occur not how fast it will occur Reaction rates are determined by collision frequency, orientation, and probability reactants have sufficient energy to overcome a barrier (energy needs to be put into collision to overcome other bond energies …at least….activation barrier Rate expressions relate how fast a reactant is consumed or product formed……gives information on microscopic details of the reaction (atomic dance partners)
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2 Again Reaction Rates t R R Δ Δ = t P P Δ Δ = 2HI (g) H 2(g) + I 2(g) t H t HI or t H t HI Δ Δ = Δ Δ Δ Δ = Δ Δ ] [ ] [ 2 1 ] [ 2 ] [ 2 2 aA + bB cC + dD Unique to reaction sequence that affects rate: t ] D [ d 1 t ] C [ c 1 t ] B [ b 1 t ] A [ a 1 Δ Δ = Δ Δ = Δ Δ = Δ Δ Microscopic (Atomic Level) Mechanisms for Reactions Bimolecular Æ Orientation Dependent For example: } Ineffective Collision – wrong orientation Unimolecular Reaction – No orientation factor…depends only on [R] ALL REACTIVE “CROSSINGS” (TO PRODUCTS) MUST HAVE SUFFICIENT ENERGY TO BREAK BONDS NEEDED TO FORM PRODUCTS Æ OVERCOME ACTIVATION BARRIERS Unimolecular Reactions --- Probabilities of Reactions Molecules react with a certain probability Æ Probability to have sufficient energy in
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This note was uploaded on 04/18/2011 for the course CHM 151 taught by Professor Dong during the Winter '08 term at University of Toronto.

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Lecture13 - Kinetics: Rates and Mechanisms of Chemical...

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