Chpt 12 Lec - Chemistry 8/e Steven S Zumdahl and Susan A...

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Chapter 12: Chemical Kinetics 1 Chemistry 8/e Steven S. Zumdahl and Susan A. Zumdahl
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Chapter Contents Introduction Rates of Reactions Differential Reaction Rate Laws Experimental Determinations Integrated Rate Laws 0 th Order 1 st Order & ½ Life 2 nd Order Multiple Reactants Reaction Mechanisms Models for Kinetics Catalysis 2
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Three most basic questions of chemistry: will something react, if they do what will you get and how fast will it go. This is about how fast will it go KINETICS 3
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Kinetics of processes have appeared before: Kinetic Theory has been invoked several times. In the origin of pressure As van der Waal’s pressure correction As a justification for Raoult’s Law In the development of the Mass Action Law 4 Kinetics
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The speed with which chemical reactions proceed is governed by two things: The rate at which reactants come into one another’s proximity (“collide”) and The probability that any given collision will prove effective in turning reactants to products. We look first at the macroscopic measurement of reaction rates. 5 Kinetics
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Change of Concentration in Time Reactants vanish in time, so [reactant] is a falling function of t . Likewise [product] is a rising function of t . The shape of these functions tells us about concentration dependence. 6 0 0 Time Concentration A B [A] 0 [A] [B] t
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Representation of the Reaction of 2NO 2 (g) → 2NO(g) + O 2 (g) 7 t=0
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Concentrations change during a reaction: [reactants] goes down [products] goes up Rate is how fast they go up or down. 8
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The rate is dependent on concentration. Here, rate = - [NO 2 ]/ t Or, Rate = [NO]/ t Or Rate = [O 2 ]/ t 9
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The rate is dependent on concentration. In general, rate is proportional to concentrations taken to some power For example, here - [NO 2 ]/ t = k[NO 2 ] n Called the rate law. k is called the rate constant, and its value can vary depending on how the rate is defined. 10
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Ask the question the other way around: At t > 0 are there additional complications? Sure! At the very least, the reverse reaction of products to produce reactants changes the rate of loss of A. 11
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