09_-_Kinetics

09_-_Kinetics - ChE102:ChemistryforEngineers...

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ChE 102: Chemistry for Engineers 14.1-14.11 – Chemical Kinetics
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2 Chemical kinetics – describe how fast a reaction occurs Consider the reaction: 2 SO 2 ( g ) + O 2 ( g ) 2 SO 3 ( g ) Rate of change in concentration of reactants and products: [ ] [ ] [ ] t SO formation SO of Rate t O n consumptio O of Rate t SO n consumptio SO of Rate d d d d d d 3 3 2 2 2 2 = = = SO 2 O 2 SO 3 time Concentration What is: Chemical Kinetics? 09 - Chemical Kinetics
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3 2 SO 2 ( g ) + O 2 ( g ) 2 SO 3 ( g ) Define the rate of reaction (r) as : For a generic reaction: a A + b B c C + d D = - = - = s L mol t SO t O t SO r d ] [ d 2 1 d ] [ d d ] [ d 2 1 3 2 2 [ ] [ ] [ ] [ ] t D d t C c t B b t A a r d d 1 d d 1 d d 1 d d 1 = = - = - = Rates of Reaction 09 - Chemical Kinetics
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4 Simple experimental set-up for determining the rate of decomposition of H 2 O 2 (aq) Oxygen gas is trapped and its volume is measured in the burette Amount of H 2 O 2 consumed and the remaining concentration of H 2 O 2 can be calculated from the measured volume of O 2 (g) H 2 O 2 ( aq ) → H 2 O ( l ) + ½ O 2 ( g ) Measuring Rates of Reaction 09 - Chemical Kinetics
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5 The slope of the [H 2 O 2 ] x time curve (red line) gives the rate of reaction. Measuring Rates of Reaction H 2 O 2 ( aq ) → H 2 O ( l ) + ½ O 2 ( g ) 09 - Chemical Kinetics
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6 Rate of Reaction of H 2 O 2  Decomposition 09 - Chemical Kinetics
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7 Rate Laws: relate the rate of reaction to the concentration of reactants are generally empirical and cannot be derived from the stoichiometry of reactions (except for some special cases that we will discuss later) Differential rate laws of a reaction: A + B products is generally stated as: k : reaction rate constant ( function of temperature ) n : order of reaction with respect to A m : order of reaction with respect to B n + m : overall order of reaction Differential Rate Laws m n B A k t a r ] [ ] [ d A] [ d 1 = - = 09 - Chemical Kinetics
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8 Important! For a given reaction: a A + b B products n is not necessarily equal to a m is not necessarily equal to b n and m must be determined experimentally Differential Rate Laws 09 - Chemical Kinetics
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9 For example, the reaction rate for: H 2 + I 2 2 HI is determined to be: r = k [H 2 ][I 2 ] while the rate for the very similar reaction , H 2 + Br 2 2 HBr is found to be : r = k [H 2 ][Br 2 ] 1/2 Differential Rate Laws – for example 09 - Chemical Kinetics
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10 If concentration is measured in mol/L and time in seconds, what are the units of the rate constants, k , for the following reactions: a) 1 st order reaction b) 2 nd order reaction ( a) 1/s b) L/mol·s ) Example 1 09 - Chemical Kinetics
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11 Use the data in the table to obtain the rate law for the decomposition of N 2 O 5 , using a differential rate law. N
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This note was uploaded on 09/17/2011 for the course CHE 102 taught by Professor Simon during the Spring '08 term at Waterloo.

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09_-_Kinetics - ChE102:ChemistryforEngineers...

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