Chapter 4 handouts

Chapter 4 handouts - Chapter 4 The Study of Chemical...

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Chapter 4 The Study of Chemical Reactions
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Chapter 4 2 Reaction Mechanism Series of discrete single steps that constitute the overall reaction. Free radical chlorination of methane will be used as an example Mechanism of a reaction is an important piece of knowledge. How do we elucidate mechanisms?
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Chapter 4 3 Tools for Study • To determine a reaction’s mechanism , look at: ¾ Equilibrium constant ¾ Free energy change ¾ Enthalpy ¾ Entropy ¾ Bond dissociation energy ¾ Kinetics ¾ Activation energy
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Chapter 4 4 Chlorination of Methane • Requires heat or light for __________. • The most effective wavelength is blue, which is absorbed by ___________. • Lots of product formed from absorption of only one _________ of light (__________). C H H H H + Cl 2 heat or light C H H H + HCl
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Chapter 4 5 Free-Radical Chain Reaction • _______ generates a reactive intermediate. • _________: the intermediate reacts with a stable molecule to produce another reactive intermediate (and a product molecule). • _________: side reactions that destroy the reactive intermediate.
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Chapter 4 6 Initiation Step A chlorine molecule splits ___________ into chlorine ________ (free radicals) Cl + photon ( h ν ) + Note the use of “fish hook” curved arrows to indicate how single electrons move during bond making and bond breaking. electron pair movement single electron movement
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Chapter 4 7 Propagation The initiation step is followed, in this reaction, by two propagation steps. Each of these generates a reactive intermediate that goes back into the sequence and keeps the reaction going.
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Chapter 4 8 Propagation Step (1) The chlorine atom collides with a methane molecule and abstracts (removes) a H, forming another _________ and one of the __________ (HCl).
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Chapter 4 9 Propagation Step (2) The methyl free radical collides with another chlorine molecule, producing the other product (methyl chloride) and regenerating a chlorine radical. =>
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Chapter 4 10 Overall Reaction C H H H H Cl + C H H H + HC l C H H H + C H H H + C H H H H + C H H H + l => + photon ( h ν ) +
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Chapter 4 11 Termination Steps • Collision of any two _________ • Combination of free radical with __________ or collision with wall.
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This note was uploaded on 04/08/2008 for the course CHEM 223 taught by Professor Pearson during the Fall '07 term at Case Western.

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Chapter 4 handouts - Chapter 4 The Study of Chemical...

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