Electrochem Lecture Notes

Electrochem Lecture Notes - 1 Electrochemistry Two major...

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Unformatted text preview: 1 Electrochemistry Two major electrochemical types: Voltaic (galvanic) cells: Voltaic (galvanic) cells: Voltaic (galvanic) cells: Voltaic (galvanic) cells: Using spontaneous chemical reactions to do work (i.e. provide electricity). Electrolytic Cells: Electrolytic Cells: Electrolytic Cells: Electrolytic Cells: Using electricity to force nonspontaneous reactions. Purification of Metals Electroplating Electrochemistry is also tied to Gibbs Free Energy and Chemical Equilibrium Oxidation-Reduction: The Heart of Electrochemistry General Idea: Since redox reactions involve the transfer of electrons from one component of a reaction to another, intercepting that transfer (flow) of electrons, allows useful “work” to be done (i.e. electrical circuits can be powered). Don’t Forget: Leo Goes Ger L oses E lectrons O xidized G ains E lectrons R educed Expanded Definition of Redox Reactions Oxidation: Oxidation: Oxidation: Oxidation:-Lose electrons-Gain oxygen (special case)-Lose hydrogen (special case) Reduction: Reduction: Reduction: Reduction:-Gain electrons-Lose oxygen (special case)-Gain hydrogen (special case) Ex. Ex. Ex. Ex. Cu (s) + 2AgNO 3(aq) → Cu(NO 3 ) 2(aq) + 2Ag (s) In this example copper loses two electrons and each silver atom gains an electron Cu → Cu 2+ + 2e- and is considered oxidized This is the oxidation half-reaction. It only shows the component oxidized and does not include any spectator ions. 2Ag + + 2e- → 2Ag and is considered reduced This is the reduction half-reaction. It only shows the component reduced and does not include any spectator ions. Net Ionic: Cu (s) + 2Ag + (aq) → Cu 2+ (aq) + 2Ag (s) Characteristics:-Electrons are lost/gained by particles in the reaction-There must be a change in “oxidation number”.-You must know the rules for assigning oxidation numbers-Oxidation numbers are for “book keeping purposes” and may not represent actual charges-Oxidations and reductions must occur in pairs (i.e. electron loss must be accompanied by electron gain)-The oxidizing “agent” does the oxidizing and is itself reduced (agent refers to entire species)-The reducing “agent” does the reducing and is itself oxidized.-In a disproportionation reaction, an element in one oxidation state is simultaneously oxidized and reduced. 2 Common Common Redox Redox Reactions Reactions Single Replacement (A + BC Single Replacement (A + BC Single Replacement (A + BC Single Replacement (A + BC → B + AC): B + AC): B + AC): B + AC): Cu (s) + 2AgNO 3(aq) → Cu(NO 3 ) 2(aq) + 2Ag (s) Combustion (hydrocarbon + O Combustion (hydrocarbon + O Combustion (hydrocarbon + O Combustion (hydrocarbon + O 2 → CO CO CO CO 2 + H + H + H + H 2 O): O): O): O): CH 4(g) + 2O 2(g) → CO 2(g) + 2H 2 O (g) Redox Redox Redox Redox Reactions in acid/base aqueous medium: Reactions in acid/base aqueous medium: Reactions in acid/base aqueous medium: Reactions in acid/base aqueous medium: 14H + (aq) + Cr 2 O 7 2- (aq) + 6Fe 2+ (aq) → 2Cr 3+ (aq) + 7H 2...
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This note was uploaded on 12/07/2011 for the course CHEM 100 taught by Professor Feebeck during the Fall '10 term at Purdue.

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Electrochem Lecture Notes - 1 Electrochemistry Two major...

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