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CHEM 1A03 (173)


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David Brock

Electrochemistry (Chapter 20) Electrochemical Cells - Separate the half cell reactions , don’t allow them to physical come in contact with each other - Beaker: one side – Cu anode, another side – Ag = cathode - Connect wire through voltmeter / electrical thing from one side to the other - Electrons need to travel from one side to the other - Salt solution – ions of salt bridge filled with KNO3, K+ follows electrons, NO3= goes away from electrons, keeps electrical neutrality - Two connected half cells - The 2 half reactions are separated yet connected electrically (salt bridge, external wire) - Solid metals = electrodes (anode, cathode) - Movemen tof e= from anode to cathode generates voltage - Movement of cation and anions thorough salt bridge maintains electrroneutrality in solution n+ - Oxidation (anode): surface of electrode erodes as M are produced, n e= then travel to cathode; M  M + n e-+ n+ n+ - Reduction (cathode): cathode gains mass as M ions gain n e= and form M(s); M + n e-  M - Oxidation: occurs at anode (Cu) Cu(s) --. Cu2+ (aq) + 2e- - Reduction: occurs at cathode (Ag) 2Ag+(aq) + 2e- --. 2Ag(s) - “ an ox and a red cat”, or vowels (O,A) / consonants (C, R) - Overall cell reaction: Cu(s) + 2Ag+(aq)  Cu2+(aq) + 2Ag(s) - Galvanic (voltanic) cells: result form spontaneous chemical reactions - Electrolytic cell: use electricity to accomplish non-spontaneous chemical change - sometimes an electrode is inert (does not chemically participate, but is needed for electron transfer to occur) Standard Electrode Potentials - absolute half-cell potentials cannot be measured - all pontentials are measured relative to the standard hydrogen electrode (SHE) assigned a potential of 0V, E◦ = exactly 0 volt - 2H+ (a=1) + 2e-   h2 (g, 1 bar); simplify: a = 1 becomes [H+] = 1M; 1 bar = I atm - Standard electrode potentials (E) report tendency for reduction to occur (Ered) - Standard conditions: conc = 1M, pres - iF E cell I pos – galvanic / spontaneous - Ecell > 0 = spontaneous - E cell = E red + E ox - I clicker 3 ansewr – a Reactions are spontaneous in one direction not spontaneous in the other Spontaneity: Ecell and ΔG - Electromotive force or cell potential (Ecell)
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