Ch15_Part1_062711 - Chapter #15 Chemical Kinetics 15.1)...

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15.1) Reaction Rates 15.2) Rate Laws: Introduction 15.3) Determining the Form of the Rate Law 15.4) Integrated Rate Law 15.5) Rate Laws: Summary 15.6) Reaction Mechanisms 15.7) The Steady-State Approximation 15.8) A Model for Chemical Kinetics 15.9) Catalysis Chapter #15 – Chemical Kinetics
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Why do we study reaction kinetics? To fully understand or apply any chemical reaction, we must know more than just the identities of the reactants and the products. We must know: if the reaction will occur (is it thermodynamically favorable?) how long it will take to occur (is it kinetically feasible?) how it will occur (what is the reaction mechanism?)
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Figure 15.1 Example: 2NO 2 (g) 2NO(g) + O 2 (g) What happens during a chemical reaction? 300 o C Reactants are used up and products are formed The reaction takes time The final concentrations approach those on the right-hand side of the figure The rate of change of a molecule’s concentration (i.e. the slope) changes with time
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2NO 2 (g) 2NO(g) + O 2 (g) The Rate is the Change in Concentration per Unit Time Rate of consumption of NO 2 = - ∆[NO 2 ]/∆t Rate of production of NO = +∆[NO]/∆t Rate of production of O 2 = +∆[O 2 ]/∆t As ∆t approaches zero, the instantaneous rate becomes the tangent: - d [NO 2 ]/ d t 2NO 2 (g) 2NO(g) + O 2 (g)
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Typically, we’re interested in the RATE OF THE REACTION For the reaction: 2 NO 2 (g) 2 NO(g) + O 2 (g) Rate = - d [NO 2 ] = d [NO] = d [O 2 ] 2 d t 2 d t d t The rate of change of concentration of each species is divided by its coefficient in the balanced chemical equation. Rates of change of reactants appear with negative signs . Product rates appear with positive signs .
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Types of Rate Laws Rate = k [A] 2 Reaction: aA products Differential Rate Law: Rate as a function of the concentration of the reactants Typically referred to simply as the “rate law” Example: [A] t = - k t + [A] o Integrated Rate Law: Concentrations as a function of time Example:
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Choosing which rate law to determine: Differential and integrated rate laws ALWAYS related Depends on what type of data is easiest to collect Rate vs. concentration Concentration vs. time Why do we care?!? Experimentally determine the rate law
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Ch15_Part1_062711 - Chapter #15 Chemical Kinetics 15.1)...

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