chapter 14 - Chapter 14 Chemical Kinetics Kinetics Studies...

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Chapter 14 Chapter 14 Chemical Kinetics Chemical Kinetics
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Kinetics Studies the rate at which a chemical process occurs. Besides information about the speed at which reactions occur, kinetics also sheds light on the reaction mechanism (exactly how the reaction occurs).
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Kinetics Remember : Thermodynamics is only interested in the initial and final states of a system.
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Kinetics is the study of how fast chemical reactions occur. There are 4 important factors which affect rates of reactions: reactant concentration, temperature, action of catalysts, and surface area. Factors that Affect Reaction Factors that Affect Reaction Rates Rates
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Factors That Affect Reaction Rates Physical State of the Reactants In order to react, molecules must come in contact with each other. The more homogeneous the mixture of reactants, the faster the molecules can react.
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Factors That Affect Reaction Rates Concentration of Reactants As the concentration of reactants increases, so does the likelihood that reactant molecules will collide.
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Factors That Affect Reaction Rates Temperature At higher temperatures, reactant molecules have more kinetic energy, move faster, and collide more often and with greater energy.
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Factors That Affect Reaction Rates Presence of a Catalyst Catalysts speed up reactions by changing the mechanism of the reaction. Catalysts are not consumed during the course of the reaction.
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Reaction Rates Rates of reactions can be determined by monitoring the change in concentration of either reactants or products as a function of time.
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Reaction Rates
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At t = 0 (time zero) there is 1.00 mol A (100 red spheres) and no B present. At t = 20 min , there is 0.54 mol A and 0.46 mol B. At t = 40 min , there is 0.30 mol A and 0.70 mol B. Reaction Rates Reaction Rates
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Calculating , Reaction Rates Reaction Rates ( 29 ( 29 ( 29 mol/min 026 . 0 min 0 min 10 mol 0 mol 26 . 0 min 0 min 10 0 at B of moles 10 at B of moles B of moles rate Average = - - = - = - = = = t t t
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Change of Rate with Time (UNITS) Most useful concentration units for rates is the molarity . Since volume is constant, molarity and moles are directly proportional. Pressure can also be used for reactions in the gas phase. Units can be in atmospheres or torrs,… Reaction Rates Reaction Rates
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Reaction Rates In this reaction, the concentration of butyl chloride, C 4 H 9 Cl, was measured at various times.
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Notice a decrease in rate as Notice a decrease in rate as the reaction proceeds the reaction proceeds
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Reaction Rates The average rate of the reaction over each interval is the change in concentration divided by the change in time: Average rate =
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Reaction Rates Note that the average rate decreases as the reaction proceeds. This is because as the reaction goes forward, there are fewer collisions between reactant molecules.
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Reaction Rates A plot of concentration vs.
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This note was uploaded on 09/06/2009 for the course CHEM chem 1B taught by Professor Valentin during the Spring '09 term at Evergreen Valley.

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chapter 14 - Chapter 14 Chemical Kinetics Kinetics Studies...

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