Chapter 13 - CH302 Chapter 13 Chemical Kinetics 1 CHEMICAL...

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1 CH302 Chapter 13 Chemical Kinetics 2 CHEMICAL KINETICS Chemical *inetics is the study of the rates of chemical reactions . ! Rates of a reaction are ratios of quantity change over a period of time. ! The ratio is defined as the time involved for reactants to be used up and the products to be formed. 3 CHEMICAL KINETICS Chemical *inetics is concerned 4ith5 ! the rates of a reaction ! the factors that affect reaction rates ! the mechanism by which reactions occur ! that is, the series of steps that the reaction undergoes.
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4 CHEMICAL KINETICS ! When we study thermodynamics: we will learn to predict whether a reaction is favorable to occur. ! However, thermodynamics does not indicate whether a favorable reaction will occur slowly or quickly± this is kinetics. 5 Rate of a Reaction Units: Moles per liter per unit time: mol L • time mol = molarity = M L M • time–1 6 Rate of a Reaction Rates are determined by ! Analyzing either concentration of reactants or products over a period of time. ! Slow reactions assay products by different techniques ! titrations, assaying for formation of acidic or basic products or ppt. ! quenching rxn, quickly cooling a sample of the reactant or product, or ! spectrophotometry, measuring color changes ! measuring pressure increase of the formation of a gas (holding the volume and temperature constant)
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7 Rate of a Reaction ! Rates of reactions are described by5 aA 9 bB ! cC 9 dD < = > represent the concentration of a substance rates the reactants disappear rates the products appear [ ] [ ] ! " # # ! ! " # " ! ! [ ] [ ] $ % # # ! ! $ # $ ! ! 8 Rate of a Reaction Ho4e±er² 4e must be concerned 4ith the stoichiometry of the reaction. ! for every a mol/L of [A] that disappears, b mol/L of [B] should disappear ! likewise, for every c mol/ L that [C] appears, d mol/L of [D] appears 1 [ ] 1 [ ] ! " & # # ! ! " # " ! ! 1 [ ] 1 [ ] $ % ( # ) # ! ! $ # $ ! ! 9 Rate of a Reaction e.g. ³or the reaction5 2 F 2 O ´ IgK ! µ FO 2 IgK 9 O 2 IgK 5 2 2 2 [ ] [ ] [ ] 1 1 1 2 4 1 * + *+ + # # # ! ! ! " # $ # $ ! ! !
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10 Rate of a Reaction The following chemical equation shows the production of NO and H 2 O by oxidizing NH 3 . At a given time, NH 3 is reacting at a rate of 1.10 M/min. 4 FH 3 9 h O 2 " 4 FO 9 N H 2 O a) At the same time, which is the rate at which the other reactant is changing and the rate at which each product is changing? b) What is the overall rate of the reaction? 11 Rate of a Reaction a) The rate at which the other reactant is changing and the rate at which each product is changing: 3 2 2 [ ] [ ] [ ] 1 1 1 [ ] 1 4 5 4 6 *, + , + *+ -&#. /0 -.&(#1/2 # # # # ! ! ! ! # " # " # $ $ ! ! ! ! 3 2 2 3 1.10 5 1.38 min 4 min 3/4 *, 3/4 + 5 -&#. /0 )16&77.&-&2(. /0 + 8 3/4 *, % & % & # # ( ( ) *) * 3 3 1.10 4 1.10 min 4 min 3/4 *, 3/4 *+ 5 -&#. /0 &77.&-&2(. /0 *+ 8 3/4 *, % & % & # # ( ( ) * 3 2 2 3 1.10 6 1.65 min 4 min 3/4 *, 3/4 , + 5 -&#. /0 &77.&-&2(. /0 , + 8 3/4 *, % & % & # # ( ( ) * 12 Rate of a Reaction b) The overall rate of the reaction? ! ±ou may choose any reactant or product to calculate the rate of the reaction: ²or² 3 3 [ ] 1.10 1 1 0.275 4 4 min min *, 5 *, 5 -&#. /0 -.&(#1/2 # ! % & # # # ( ! ) * 2 2 1 [ ] 1 1.38 0.276 5 5 min min + 5 + 5 -&#. /0 -.&(#1/2 # ! % & # # # ( !
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This test prep was uploaded on 03/19/2008 for the course CH 302 taught by Professor Holcombe during the Fall '07 term at University of Texas at Austin.

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Chapter 13 - CH302 Chapter 13 Chemical Kinetics 1 CHEMICAL...

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