Lecture16 - 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 aligment) 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 Reaction rate constants relate probability that the molecules have energy in the correct atomic motions (modes) to react Increased temperature increases the energy into kinetic, rotational, and vibrational degrees of freedom --- increases the probability that the molecules will have energy in the correct atomic motions to react Temperature effects can be quantitatively connected through Arrenhius equation: k = Ae -Ea/RT ; A = frequency of sampling activation barrier and exp(-Ea/RT) gives probability of having sufficient energy to go over barrier Activation Energy Diagrams… give relative energies for reactants, activation energy or transition state, and products Le Chatelier’s principle makes sense re: relative activation barriers for exothermic and endothermic reaction connection of kinetics to thermodynamics Chain reactions……multiplier factor in reaction rates
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2 Accelerating Reactions What can be altered to speed up a reaction? Increase Concentration http://scidiv.bcc.ctc.edu/wv/7/0007-005-rea-t-cat.html Increase Temperature Increase Surface Area htp:/wps.prenhal.com/wps/media/objects/602/616516/Chapter_14.html Use a Catalyst Use a Catalyst Catalysts A substance that increases rate by lowering the activation energy (provides alternative rxn mechanism). Reaction Progress Energy reactants reactants products products E a, regular 0 E a, catalysed a, catalysed Homogeneous Catalysts Same phase as the reactants. Example: 2H 2 O 2(aq) H 2 O (l) + O 2(g ) Br 2(aq) + H 2 O 2(aq) 2Br - (aq) + 2H + (aq) + O 2(g) 2Br - (aq) + H 2 O 2(aq) + 2H + (aq) Br 2(aq) + H 2 O (l) The catalyst appears as both reactant and product, The catalyst appears as both reactant
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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- Toronto.

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Lecture16 - Kinetics: Rates and Mechanisms of Chemical...

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