Chapter 16 - Chapter 16 Kinetics: Rates and Mechanisms of...

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Unformatted text preview: Chapter 16 Kinetics: Rates and Mechanisms of Chemical Reactions Kinetics: Rates and Mechanisms of Chemical Reactions 16.1 Factors That Influence Reaction Rate 16.2 Expressing the Reaction Rate 16.3 The Rate Law and Its Components 16.4 Integrated Rate Laws: Concentration Changes over Time 16.7 Reaction Mechanisms: Steps in the Overall Reaction 16.8 Catalysis: Speeding Up a Chemical Reaction 16.5 The Effect of Temperature on Reaction Rate 16.6 Explaining the Effects of Concentration and Temperature Factors That Influence Reaction Rate Under a specific set of conditions, every reaction has its own characteristic rate, which depends upon the chemical nature of the reactants. Four factors can be controlled during the reaction: 1. Concentration - molecules must collide to react; 2. Physical state - molecules must mix to collide; 3. Temperature - molecules must collide with enough energy to react; 4. The use of a catalyst. Collision energy and reaction rate. Expressing the Reaction Rate reaction rate - changes in the concentrations of reactants or products per unit time reactant concentrations decrease while product concentrations increase Rate of reaction = - for A B change in concentration of A change in time = - conc A 2 - conc A 1 t 2 - t 1 (conc A)- t Concentration of O 3 at Various Times in its Reaction with C 2 H 4 at 303 K C 2 H 4 ( g ) + O 3 ( g ) C 2 H 4 O( g ) + O 2 ( g ) Time (s) Concentration of O 3 (mol/L) 0.0 20.0 30.0 40.0 50.0 60.0 10.0 3.20x10-5 2.42x10-5 1.95x10-5 1.63x10-5 1.40x10-5 1.23x10-5 1.10x10-5 (conc A)- t The concentration of O 3 vs. time during its reaction with C 2 H 4 . C 2 H 4 ( g ) + O 3 ( g ) C 2 H 4 O( g ) + O 2 ( g )- [C 2 H 4 ] t rate = - [O 3 ] t = Plots of [C 2 H 4 ] and [O 2 ] vs. time. Tools of the Laboratory In general, for the reaction a A + b B c C + d D rate = 1 a- = - [A] t 1 b [B] t 1 c [C] t = + 1 d [D] t = + The numerical value of the rate depends upon the substance that serves as the reference. The rest is relative to the balanced chemical equation. Expressing Rate in Terms of Changes in Concentration with Time PROBLEM: Because it has a nonpolluting product (water vapor), hydrogen gas is used for fuel aboard the space shuttle and may be used by earthbound engines in the near future. 2H 2 ( g ) + O 2 ( g ) 2H 2 O( g ) (a) Express the rate in terms of changes in [H 2 ], [O 2 ], and [H 2 O] with time. (b) When [O 2 ] is decreasing at 0.23 mol/L*s, at what rate is [H 2 O] increasing? Determining Reaction Order from Rate Laws PROBLEM: For each of the following reactions, determine the reaction order with respect to each reactant and the overall order from the given rate law....
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This note was uploaded on 12/03/2010 for the course CHEM 1035 taught by Professor Jgdillard during the Fall '07 term at Virginia Tech.

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Chapter 16 - Chapter 16 Kinetics: Rates and Mechanisms of...

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