Lec-06-Chap14-2-bare

Lec-06-Chap14-2-bare - Lec-06-Chap14-2-bare Lec-06 Reaction...

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Lec-06-Chap14-2-bare 9/14/2011 Chemical Kinetics Rect. Mechanisms. Arrhenius Eq., etc. 1 Review for the First Midterm Monday, September 19, from 6:40 to 9:40 PM Room Harriman Hall 137 1 Lec-06: Reaction Mechanism and Rate Laws Chapter 14 The rate law cannot be inferred from the overall balanced equation because the rate law is a consequence of the detailed mechanism of the reaction. The overall reaction equation describes the identity and proportions in which the reactant species are consumed and the identity and proportions in which the product species are generated . 2 Chemical reactions, described by stoichiometric “overall” equations: + A CD B cd ab Overall balanced equation           rate constant AC AB 11 rate = t tt t mn dd t a dt c d k t  Rate for Chemical Reaction. Rate Law
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Lec-06-Chap14-2-bare 9/14/2011 Chemical Kinetics Rect. Mechanisms. Arrhenius Eq., etc. 2 The Rate Law The exponents m, n, … can be integers or fractions (positive or negative). 3       rate constan reactanct concentrati t ons instantaneous =rate A rate B mn tt k t    + A CD B cd ab m: order of the reaction with respect to substance A. n: order of the reaction with respect to substance B. order of the reaction  The rate constant k is a constant : it does not change with time, or with the concentrations of reactants and products. It does change, however, when we change the temperature. Dependence of the rate constant with temperature The Arrhenius Equation More energy is available to the reaction system as the temperature increases. E a is the activation energy (units of molar energy, J mol –1 ) R is the gas constant (J K –1 mol –1 ) T is the temperature (K) 4   frequency factor (same u rate nits constant as ) a k E RT A e kT This leads to a temperature dependence of the rate constant . Experimentally Arrhenius found: 11 8.314JK mol R 
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Lec-06-Chap14-2-bare 9/14/2011 Chemical Kinetics Rect. Mechanisms. Arrhenius Eq., etc. 3 Dependence of the rate constant with temperature The Arrhenius Equation   ln units of kT k    1 T slope = a E
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Lec-06-Chap14-2-bare - Lec-06-Chap14-2-bare Lec-06 Reaction...

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