Chem_215_Lect_31_Color - - Need a flame or spark to...

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1 Catalyst • provides a new reaction pathway of lower activation energy • involved in a reaction without undergoing permanent change • is not a reactant or product 2 Types of Catalysts : 1. Homogeneous Catalysts: single phase (usually in solution) HCOOH (aq) CO (g) + H 2 O (l)
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2 1. Homogeneous Catalysts: single phase (usually in solution) HCOOH (aq) CO (g) + H 2 O (l) 2. Heterogeneous Catalysts: solid in presence of gas or liquid. 2CO + 2NO 2CO 2 + N 2 a) Adsorption b) Dissociation c) Reaction and Desorption
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3 2CO + 2NO 2CO 2 + N 2 a) Adsorption b) Dissociation c) Reaction and Desorption Potential Energy Diagram
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4 Catalyst • provides an alternative reaction pathway of lower activation energy • participates in a reaction without undergoing permanent change • Is not a reactant or product Demo: Combustion of Hydrogen: 2H 2 + O 2 2H 2 O Reaction involves a Free Radical Mechanism Free Radical: - Atom or molecule with an unpaired electron - Highly reactive Initiation: H 2 (g) + O 2 (g) HO 2 (g) + H (g) - Large activation energy (E g ) for gas phase initiation
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Unformatted text preview: - Need a flame or spark to initiate reaction 5 Combustion of Hydrogen: 2H 2 + O 2 2H 2 O Reaction involves a Free Radical Mechanism Free Radical:- Atom or molecule with an unpaired electron- Highly reactive Initiation: H 2 (g) + O 2 (g) HO 2 (g) + H (g) - Large activation energy (E g ) for gas phase initiation- Need a flame or spark to initiate reaction large activation energy (E g ) in gas phase Need a flame or spark to initiate reaction Small activation energy (E s ) in surface catalyzed reaction Initiation occurs at room temperature 6 For H 2 + O 2 HO 2 + H on Pt (heterogeneous) a) Adsorption: Pt surface H-H H H Adsorbed Hydrogen b) Surface Reaction H H O=O HO 2 H Adsorbed Products c) Desorption HO 2 H HO 2 H 7 Ozone Cycle Formation/Photodissociation O 2 + h 2O O + O 2 + M O 3 + M O 3 + h O 2 + O Cl Catalyzed Destruction Cl + O 3 ClO + O 2 ClO + O Cl + O 2 _______________ O + O 3 2O 2...
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Chem_215_Lect_31_Color - - Need a flame or spark to...

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