CHM152Chapter 12

Chemistry (MasteringChemistry Series)

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8/27/2009 1 Chapter 12 Chemical Kinetics 12.1 Kinetics ` The study of rates of reactions and reaction mechanisms (e.g., how fast a reaction will go and what steps it goes through) ` What is rate? ` Definition of reaction rate: the change in concentration of a reactant or product over change in time →Δ [A] / Δ t 12.1 Factors that Affect Rate ` Concentrations ` Temperature ` Pressure ` Catalysts ` Surface area
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8/27/2009 2 2NO 2 (g) 2NO (g) + O 2 (g) ` How can rate be represented on a graph? ` What happens to NO 2 over time? NO? O 2 ? ` How can their rates be expressed relative to each other? 12.1 Graph of Reaction 12.1 Relative Rates ` Rate of NO 2 consumption = Rate of NO production = 2 × Rate of O 2 production ` Then t ] O [ t 2 NO] [ t 2 ] NO [ 2 2 Δ Δ = Δ Δ = Δ Δ t ] O [ 2 t NO] [ t ] NO [ 2 2 Δ Δ = Δ Δ = Δ Δ
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8/27/2009 3 12.1 Relative Rates ` If NO 2 is disappearing at a rate of 4.2 x 10 -5 M/s, what is the rate of appearance of O 2 ? t ] [O t ] NO [ 2 1 2 2 Δ Δ = Δ Δ ` Write the rates of the species in the following reaction: 5Br - + BrO 3 - + 6H + 3Br 2 + 2H 2 O Group Quiz #1 ` According to the following unbalanced reaction, if the rate of appearance of oxygen gas is 4.00 x 10 -2 M/s, what is the rate of disappearance of KClO 3 (g)? KClO 3 (g) KCl(g) + O 2 (g) 12.2 Rate Laws & Reaction Order ` What happens to a chemical reaction over time? ` Over time, the change in concentration will depend on the forward and reverse reactions. ` To simplify things, choose conditions before products become significant ` This allows us to examine rates using only reactants
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8/27/2009 4 12.2 Rate Laws ` Reaction: ` aA + bB Æ Products ` Rate Law: n m B A k Rate ] [ ] [ = ` k is Rate Constant ` m & n are the order of reactants (NOT the coefficient); m & n must be determined experimentally! ` Reaction Order = sum of reactant orders 12.2 Rate Laws ` Rate law of the decomposition reaction of NO 2 ` Rate = k [NO 2 ] m ` k = rate constan = rate constant ` m is order of reactant (NOT the coefficient); m must be determined experimentally ` Why do we want to determine the rate of a reaction? 12.2 Types of Rate Laws ` Differential Rate Law (or Rate Law) ` rate depends on concentration ` Integrated Rate Law m k ] NO [ t ] [NO Rate 2 2 = Δ Δ = ` rate depends on time
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8/27/2009 5 12.3 Determining the Rate Law ` 2N 2 O 5 (soln) 4NO 2 (soln) + O 2 (g) [N 2 O 5 ] Rate (M/s) 0.90 M 5.4 x 10 -4 0 45 M 27 x 10 -4 0.45 M 2.7 x 10 ` What happens to rate as concentration is halved?
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CHM152Chapter 12 - Chapter 12 Chemical Kinetics 12.1...

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