Chap16 Kinetics (5)

Chap16 Kinetics (5) - Chapter 16 Kinetics Rates and...

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Chapter 16 Kinetics: Rates and Mechanisms of Chemical Reactions
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Kinetics: Rates and Mechanisms of Chemical Reactions 16.1 Factors That Influence Reaction Rates 16.2 Expressing the Reaction Rate 16.3 The Rate Law and Its Components 16.4 Integrated Rate Laws: Concentration Changes over Time 16.7 Reaction Mechanisms: Steps in the Overall Reaction 16.8 Catalysis: Speeding Up a Chemical Reaction 16.5 The Effect of Temperature on Reaction Rate 16.6 Explaining the Effects of Concentration and Temperature
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Accelerating Reactions What can be altered to speed up a reaction? Increase Concentration http://scidiv.bcc.ctc.edu/wv/7/0007-005-rea-t-cat.html Increase Temperature Increase Surface Area http://wps.prenhall.com/wps/media/objects/602/616516/Chapter_14.html Use a Catalyst Use a Catalyst
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Catalysts A substance that increases rate by lowering the activation energy (provides alternative rxn mechanism). Reaction Progress Energy reactants reactants products products E a, regular 0 E E a, catalysed a, catalysed
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Homogeneous Catalysts Same phase as the reactants. Example: 2H 2 O 2(aq) H 2 O (l) + O 2(g ) Br 2(aq) + H 2 O 2(aq) 2Br - (aq) + 2H + (aq) + O 2(g) 2Br - (aq) + H 2 O 2(aq) + 2H + (aq) Br 2(aq) + H 2 O (l) The catalyst appears as both reactant and product, The catalyst appears as both reactant and product, so it is unchanged by the reaction. so it is unchanged by the reaction. A small amount of catalyst can last several cycles A small amount of catalyst can last several cycles and produce a large effect. and produce a large effect.
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Rate Law of a Catalysed Reaction Although the catalyst does not show up in the reaction itself, its presence is manifested in the rate law: ) g ( 2 ) aq ( CS ) aq ( 3 ) aq ( 3 N 3 I 3 N 2 I 2  Step 1 Step 1 CS 2 + N 3 - S 2 CN 3 - slow slow Step 2 Step 2 2S 2 CN 3 - + I 3 - 2CS 2 + 3N 2 + 3I - fast fast rate of I rate of I 3 - disappearance = k[CS disappearance = k[CS 2 ][N ][N 3 - ] ] So the reaction is zero order in I So the reaction is zero order in I 3 - instead 1 instead 1 st st order in the CS order in the CS 2 catalyst. catalyst.
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Kinetics and Catalysts Note: A catalyst increases the rate of a reaction without itself being consumed http://www.wmo.ch/web/arep/reports/o3_asses s_rep_2002_front_page.html RECALL:
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Reaction Mechanisms have Multiple Pathways http://www.wmo.ch/web/arep/reports/o3_a ssess_rep_2002_front_page.html
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The effect of catalysts is to either present an alternative pathway with a lower activation barrier or to form a complex that lowers the activation barrier. Mechanism of Catalysis The activation energy diagram for the reaction between O 3 and O.
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Catalysis – The Choice of Industry Most commonly, a metal surface used with Most commonly, a metal surface used with fluid (gaseous) reactions: fluid (gaseous) reactions: Fe in the Haber Fe in the Haber - - Bosch Process Bosch Process Exotic metals in H Exotic metals in H 2 cracking for fuel cells cracking for fuel cells Various suspended metals for solution Various suspended metals for solution - - based based Increasingly, Increasingly, biocatalysis biocatalysis is more popular.
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This note was uploaded on 12/15/2011 for the course CHM 139 taught by Professor Browning during the Spring '08 term at University of Toronto.

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Chap16 Kinetics (5) - Chapter 16 Kinetics Rates and...

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