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Unformatted text preview: Chapter 14 Chapter 14 Chemical Kinetics Chemical Kinetics CHEMISTRY The Central Science 9th Edition • Kinetics is the study of how fast chemical reactions occur. • There are 4 important factors which affect the rates of chemical reactions: • reactant concentration, • temperature, • action of catalysts, and • surface area. Kinetics Kinetics • The speed of a reaction is defined as the change that occurs per unit time. • It is determined by measuring the change in concentration of a reactant or product with time. • The speed the of the reaction is called the reaction rate . • For a reaction A → B • Suppose A reacts to form B. Let us begin with 1.00 mol A. Reaction Rates Reaction Rates ( 29 t ∆ ∆ = = B of moles in time change B of moles of number in change rate Average Change in Concentration of Change in Concentration of Reactions Reactions 10 20 – At t = 0 (time zero) there is 1.00 mol A (100 red spheres) and no B present. – At t = 10 min, there is 0.54 mol A and 0.26 mol B. – At t = 20 min, there is 0.30 mol A and 0.70 mol B. – Calculating, Calculating Reaction Rates Calculating Reaction Rates Using Products Using Products ( 29 ( 29 ( 29 mol/min 026 . min min 10 mol mol 26 . min min 10 at B of moles 10 at B of moles B of moles rate Average = = = = = ∆ ∆ = t t t • For the reaction A → B there are two ways of measuring rate: • the speed at which the products appear (i.e. change in moles of B per unit time), or • the speed at which the reactants disappear (i.e. the change in moles of A per unit time). • The equation, when calculating rates of reactants, is multiplied by 1 to compensate for the negative concentration. – By convention rates are expressed as positive numbers. Calculating Reaction Rates Calculating Reaction Rates Using Reactants Using Reactants ( 29 t ∆ ∆ = A of moles A respect to with rate Average • Most useful units for rates are to look at molarity. Since volume is constant, molarity and moles are directly proportional. • Consider: Reaction Rates Reaction Rates Reactants Products Reaction Rates for C Reaction Rates for C 4 4 H H 9 9 Cl Cl 4 9 Properties of C Properties of C 4 4 H H 9 9 Cl Cl Reaction Reaction Instantaneous Reaction Rates Instantaneous Reaction Rates for C for C 4 4 H H 9 9 Cl Cl • For the reaction Reaction Rates and Stoichiometry Reaction Rates and Stoichiometry [ ] [ ] t t ∆ ∆ = ∆ ∆ = OH H C Cl H C Rate 9 4 9 4 [ ] [ ] [ ] [ ] t d t c t b t a ∆ ∆ = ∆ ∆ = ∆ ∆ = ∆ ∆ = D 1 C 1 B 1 A 1 Rate •...
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This note was uploaded on 02/20/2011 for the course CHEM 101 taught by Professor John during the Spring '11 term at Caldwell College.
 Spring '11
 John
 Chemistry, Kinetics

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