lec 2 chem 6c

lec 2 chem 6c - We are now going to be using WebCT? Review:...

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Unformatted text preview: We are now going to be using WebCT? Review: Balanced a simple redox reaction Broke redox reactions into reactions Balanced a redox reaction in an acidic solution Preview: Learn how to balance a redox reaction with OH Learn the basics of a Galvanic cell Cell potential ( ) or electromotive force (emf) Standard cell potentials ( ) Faradays Law Combining Faradays Law with the equilibrium constant Lets review what we have done for redox reactions in an acidic solution: 1) Break apart oxidation and reduction reactions 2) Balance each reaction: first balance all elements other than O and H, then balance O by adding H 2 O(l) then balance H by adding H + finally balance charge by adding e- s 3) Multiply both reactions to obtain the same number of e- s in both 4) Add the two reactions together and simplify Lets now balance the redox reaction for a NiCd battery which occurs in a basic solution Given the following reaction: 8H + (aq) + MnO 4 (aq) + 5Fe 2+ (aq) & Mn 2+ (aq) + 5Fe 3+ (aq) + 4H 2 O(l) Reduction: 8H + + MnO 4 + 5e- & Mn 2+ + 4H 2 O Oxidation: 5(Fe 2+ & Fe 3+ + e- ) If this is placed in a beaker, will it run a motor? Dont copy this down!!! Just listen 8H + (aq) + MnO 4 (aq) + 5Fe 2+ (aq) & Mn 2+ (aq) + 5Fe 3+ (aq) + 4H 2 O(l) MnO 4 oxidizes Fe 2+ to form Fe 3+ MnO 4 Fe 2+ H + No electrons flow, the Fe 2+ and MnO 4 quench each other MnO 4 H + Fe 2+ Conductive Wire What about now? e- e- e- e- Charge build-up: Reaction stops quickly MnO 4 H + Fe 2+ Conductive Wire e- e- e- e- Salt Bridge A salt bridge contains strong electrolytes in a Jello-like state that alleviate charge build-up Electrons flow! Reducing Agent Oxidizing Agent MnO 4 H + Fe 2+ Conductive Wire e- e- e- e- A porous disk contains tiny holes that only partially allow ions to pass. Electrons flow! Reducing Agent Oxidizing Agent Porous Disk MnO 4 H + Fe 2+ e- e- e- e- Salt Bridge Reducing Agent Oxidizing Agent Galvanic Cell Device changing chemical energy into electrical energy Origins of Electrochemistry: Italy Luigi Galvani Vs. Alessandro Volta Galvani showed that charge could make a frogs leg jump (father of neurophysiology) Galvani also showed that two dissimilar metals placed on tissue released animal electricity as opposed to static electricity Volta believed that animal tissue was not...
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This note was uploaded on 03/21/2009 for the course CHEM 6C taught by Professor Hoeger during the Spring '08 term at UCSD.

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lec 2 chem 6c - We are now going to be using WebCT? Review:...

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