Chapter 15.docx

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Department
Chemistry & Biochemistry
Course
CHM 142
Professor
Dr.James D.Garrity
Semester
Summer

Description
Chemical Kinetics—study of rates at which reactants/products change during a reaction  Includes study of factors that affect the rate of reactions, and steps involved as a reaction proceeds Reaction rate—change in concentration of a reactant/product over time  N2 + O 2 = 2NO  Rate = -(ΔN 2/ Δt) = -( ΔO2/ Δt) = ½( ΔNO/ Δt) Average rate—change in concentration of reactant/product over a specific time interval  Average rate = ΔNO/ Δt Initial rate—instantaneous rate at time, t=0  Initial rates are used to determine the effect of reactant concentrations on reaction rates If, when the concentration of H is doubled, the rate doubles, the reaction order for H is 1. Units of k depend on the order of reaction Rate law—tells how the initial concentration of a reaction affects the rate Integrated rate law—mathematical expression describing the change in concentration of a reaction over time Half life (1/2) Integrated Rate Law: Second-Order Reaction 2NO 2 2NO + O 2  Rate = k*[NO 2]^2  Rate Law: (- Δ[NO 2]  1/[NO 2]f= kt + 1/[NO ]0 Pseudo-First-Order nd nd Integrated 2 order rate law only applies to reactions that are 2 order in a single reactant, Does not apply to a reaction that is 1 storder in 2 reactants (2nd order overall) Integration of: Rate = k[A][B] is complicated Pseudo-first-order Conditions are adjusted so that all but a single reactant are present in high concentrations, The concentrations of these reactants doesn’t change significantly during the reaction Reaction rate an be determined by the concentration of the limiting reactant. Rate=k[A][Bst st  1 order in [A], 1 order in [B]  [B] is held at a high concentration  Therefore, k[B] is a constant. o K[B] = k’  Simplified rate law  Rate = k’ [A]
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