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2046chapter20 - 1 Ch 20 Electrochemistry: the study of the...

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Unformatted text preview: 1 Ch 20 Electrochemistry: the study of the relationships between electricity and chemical reactions. In electrochemical reactions, electrons are transferred from one species to another. Learning goals and key skills: h Identify oxidation, reduction, oxidizing agent, and reducing agent in a chemical equation h Complete and balance redox equations using the method of half-reactions. h Sketch a voltaic cel and identify its cathode, anode, and the directions that electrons and ions move. h Calculate standard emfs (cel potentials), E ° cel , from standard reduction potentials. h Use reduction potentials to predict whether a redox reaction is spontaneous h Relate E o cel to Δ G ° and equilibrium constants. h Calculate emf under nonstandard conditions h Describe to reactions in electrolytic cel s h Relate the amounts of products and reactants in redox reactions to electrical charge. Review redox reactions: assigning oxidation numbers To keep track of what species loses electrons and what species gains them, we assign oxidation numbers . Assigning oxidation numbers How to determine oxidation numbers 1. Elemental form, each atom has ox. # = 0. Zn O 2 O 3 I 2 S 8 P 4 2. In simple ions, ox. # = charge on ion.-1 for Cl- +2 for Mg 2+ 3. The ox. # of F is ALWAYS -1 with all other elements. FeF 3 PF 5 SF 6 OF 2 2 Assigning oxidation numbers 4. The ox. # of O is normally -2 (except in the peroxide ion, which has an oxidation number of ¡1) and the ox. # of H is +1 (except with metals). O is -2 in NO H is +1 in CH 4 O is -1 in Na 2 O 2 H is -1 in CaH 2 5. Algebraic sum of oxidation numbers = 0 for a compound = overall charge for an ion Example Assign the oxidation numbers to each element: SiBr 4 K 3 PO 4 Cu(NO 3 ) 3 ELECTRON TRANSFERS between an electron donor and electron acceptor. Transfer leads to— 1. increase in oxidation number = OXIDATION 2. decrease in oxidation number = REDUCTION Oxidizing agent or oxidant: causes the oxidation Reducing agent or reductant: causes the reduction Redox reactions 3 Example Label the species that undergo oxidation and reduction. Also identify the oxidizing agent and reducing agent. Cu (s) + 2 AgNO 3 (aq) → Cu(NO 3 ) 2 (aq) + 2 Ag (s) Example Label the species that undergo oxidation and reduction. Also identify the oxidizing agent and reducing agent. Cu (s) + 2 Ag N O 3 (aq) → Cu( N O 3 ) 2 (aq) + 2 Ag (s) +1 +5-2 +2 +5-2 Oxidation Reduction Oxidizing agent: Ag in Ag NO 3 ; Reducing agent: Cu Label the species that undergo oxidation and reduction. Also identify the oxidizing agent and reducing agent. Cu (s) + 2 Ag N O 3 (aq) → Cu( N O 3 ) 2 (aq) + 2 Ag (s) +1 +5-2 +2 +5-2 Electron transfer reactions Essential features: • one reactant is oxidized • one reactant is reduced • the oxidizing agent is reduced • the reducing agent is oxidized • an element is oxidized if its ox # increases;...
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This note was uploaded on 12/13/2011 for the course CHM 2046h taught by Professor Lufaso during the Fall '11 term at UNF.

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2046chapter20 - 1 Ch 20 Electrochemistry: the study of the...

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