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Ek Chem 7

Electrochemistry

QuestionAnswer
oxidation losing electrons
reduction gaining electrons
atoms with a 0 oxidation state atoms in their elemental form
atoms with a -1 oxidation state fluorine group 17 elements (halogens)
atom with a +1 oxidation state hydrogen, except when bonded to a metal: then it is -1 group 1 elements
atom with a -2 oxidation state oxygen (except when it is a peroxide like H2O2) group 16 elements (oxygen family)
atoms with a +2 oxidation state group 2 elements (alkaline earth metals)
atoms with a -3 oxidation state group 15 elements (nitrogen family)
transition metal oxidation states change according to the atoms with which they are bonded
reductant reducing agent in a redox reaction, this will be oxidized
oxidant oxidizing agent in a redox reaction, this will be reduced
electric potential, E a potential associated with any redox reaction, can be separated into the oxidation and reduction component
reduction potential electric potential describing the half reaction of a redox rxn
standard reduction potential reduction potential at 25 degC - half reaction is spontaneously reduced if positive and spontaneously oxidized if negative
standard hydrogen electrode 2H+ + 2e' --> H2 (E = 0.00V) used to approximate electric potentials
strongest oxidizing agent when comparing reduction potentials this would be the one w/ the higher (more positive) reduction potential - more spontaneously reduced
strongest reducing agent when comparing reduction potentials this would be the one w/ the more negative reduction potential - more spontaneously oxidized
steps to balance redox rxn 1. divide rxn into half rxns 2. balance elements other than H and O 3. add H20 to 1 side until O balanced 4. add H+ to 1 side until H balanced 5. Add e- until charge balanced 6. multiply each half rxn to make e's eqal 7. add 2 half rxns and simplif
galvanic cell aka voltaic cell, made of multiphase series of components w/ no component occurring in more than 1 phase but all conduct electricity but 1 is impermeable to electrons *cell potential is always positive*
simple galvanic cell composed of.. 2 electrodes - anode and cathode
anode in a galvanic cell where the oxidation half rxn takes place
cathode in a galvanic cell where the reduction half rxn takes place
electromotive force (emf) aka cell potential, potential difference btw the terminals when they are not connected
standard state cell potential sum of the standard state potentials of the corresponding half reactions
salt bridge electrolyte soln that acts as the ionic conductor that is impermeable to e's (necessary for galvanic cell) - liquid junction that minimized potential diff and allows ionic conduction btw solns w/o creating strong extra potential
terminal electronic conductors (often metal wires), symbolized as T
galvanic cell symbolized - T-E-I-E'-T' where T are the terminals, E are the electrodes, and I is the ionic conductor (often salt bridge)
what would happen if a galvanic cell didn't have a salt bridge the solns of the galvanic cell would mix providing a low resistance path for e's to move from the anode to the cathode effectively short circuiting the cell and leaving it with a potential of zero
free energy and cell potential eqn delta(G) = -n*F*Emax n is the moles of e' transferred, F is Faraday's constant, E is the cell potential
positive cell potential indicates ___ free energy negative meaning rxn is spontaneous
free energy relating to reaction quotient eqn delta(G) = delta(Go) + RTln(Q) where Q = Products/Reactants
standard free energy eqn (relating to equilibrium constant) delta(Go) = -RTln(K)
what are the qualitative relationships btw K and standard free energy if K = 1, then delta(Go) = 0 if K > 1, then delta(Go) < 0 if K < 1, then delta(Go) > 0 **remember this is standard state
Nernst eqn E = Eo - (RT/nF)ln(Q) expresses the relationship btw chemical concentrations and potential difference
concentration cell limited form of galvanic cell with reduction half rxn taking place in 1 half cell and the EXACT reverse of that half rxn taking place in the other half cell, NEVER at standard conditions, requires use of Nernst eqn to solve - tend to have small potentials
in what direction will current flow in the concentration cell? think about which will create the greatest entropy - the more concentrated side will try to become less concentrated and the e's will flow accordingly
electrolytic cell has NEGATIVE emf, rxns are forced by outside power source where cathode is negative and anode is positive but reduction still takes place at cathode and oxidation at anode
Created by: miniangel918 on 2010-11-10



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