Lecture 05_Ch15a - Chapter#15 Chemical Kinetics 15.1 Reaction Rates 15.2 Rate Laws Introduction 15.3 Determining the Form of the Rate Law 15.4

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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: 2NO2(g) Ê 2NO(g) + O2(g) What happens during a chemical reaction? 300 oC Reactants are used up and products are formed The reaction takes time The final concentrations approach those on the right-hand side of the reaction equation The rate of change of a molecule’s concentration (i.e. the slope) changes with time
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2NO2(g) 2NO(g) + O2(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 [NO2]/ d t 2NO2(g) 2NO(g) + O2(g)
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Typically, we’re interested in the RATE OF THE REACTION For the reaction: 2 NO2(g) 2 NO(g) + O2(g) Rate = -(1/2) d [NO2] = (1/2) d [NO] = d [O2] d t 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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Rate Laws Rate = - d [A] = k [A] n d t Rate expressed as function of [A] k = rate constant n = order of reaction with respect to [A] k and n are determined experimentally ! Reaction: aA * products Assumes reverse reaction is negligible ( i.e. forward reaction is irreversible) Differential Rate Law Equations that show how the rate depends on the concentration of the reactants
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Determining the Form of the Rate Law Using the Method of Initial Rates For a
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This note was uploaded on 04/11/2011 for the course CHEM 162 taught by Professor N. during the Spring '08 term at University of Washington.

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Lecture 05_Ch15a - Chapter#15 Chemical Kinetics 15.1 Reaction Rates 15.2 Rate Laws Introduction 15.3 Determining the Form of the Rate Law 15.4

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