Kinetics - Chemical Kinetics Chapter 13 Chemical Kinetics...

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Chemical Kinetics Chapter 13
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Chemical Kinetics Thermodynamics – does a reaction take place? Kinetics – how fast does a reaction proceed? Reaction rate is the change in the concentration of a reactant or a product with time ( M /s). A B rate = - [A] t rate = [B] t [A] = change in concentration of A over time period t [B] = change in concentration of B over time period t Because [A] decreases with time, [A] is negative . 13.1
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A B 13.1 rate = - [A] t rate = [ B ] t time
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Br 2 ( aq ) + HCOOH ( aq ) 2Br - ( aq ) + 2H + ( aq ) + CO 2 ( g ) average rate = - [Br 2 ] t = - [Br 2 ] final – [Br 2 ] initial t final - t initial slope of tangent slope of tangent slope of tangent instantaneous rate = rate for specific instance in time 13.1
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rate α [Br 2 ] rate = k [Br 2 ] k = rate [Br 2 ] 13.1 = rate constant = 3.50 x 10 -3 s -1
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Factors that Affect Reaction Rate 1. Temperature Collision Theory: When two chemicals react, their molecules have to collide with each other with sufficient energy for the reaction to take place. Kinetic Theory: Increasing temperature means the molecules move faster. 1. Concentrations of reactants More reactants mean more collisions if enough energy is present 1. Catalysts Speed up reactions by lowering activation energy 1. Surface area of a solid reactant Bread and Butter theory: more area for reactants to be in contact 1. Pressure of gaseous reactants or products Increased number of collisions
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The Rate Law 13.2 The rate law expresses the relationship of the rate of a reaction to the rate constant and the concentrations of the reactants raised to some powers. a A + b B c C + d D Rate = k [A] x [B] y reaction is x th order in A reaction is y th order in B reaction is (x +y)th order overall
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F 2 ( g ) + 2ClO 2 ( g ) 2FClO 2 ( g ) rate = k [F 2 ] x [ClO 2 ] y Double [F 2 ] with [ClO 2 ] constant Rate doubles x = 1 Quadruple [ClO 2 ] with [F 2 ] constant Rate quadruples y = 1 rate = k [F 2 ][ClO 2 ] 13.2
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Run # Initial [A] ([A] 0 )
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