Electrochemistry
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| oxidation | losing electrons
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| reduction | gaining electrons
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| atoms with a 0 oxidation state | atoms in their elemental form
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| atoms with a -1 oxidation state | fluorine
group 17 elements (halogens)
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| atom with a +1 oxidation state | hydrogen, except when bonded to a metal: then it is -1
group 1 elements
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| atom with a -2 oxidation state | oxygen (except when it is a peroxide like H2O2)
group 16 elements (oxygen family)
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| atoms with a +2 oxidation state | group 2 elements (alkaline earth metals)
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| atoms with a -3 oxidation state | group 15 elements (nitrogen family)
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| transition metal oxidation states | change according to the atoms with which they are bonded
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| reductant | reducing agent in a redox reaction, this will be oxidized
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| oxidant | oxidizing agent in a redox reaction, this will be reduced
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| electric potential, E | a potential associated with any redox reaction, can be separated into the oxidation and reduction component
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| reduction potential | electric potential describing the half reaction of a redox rxn
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| standard reduction potential | reduction potential at 25 degC - half reaction is spontaneously reduced if positive and spontaneously oxidized if negative
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| standard hydrogen electrode | 2H+ + 2e' --> H2 (E = 0.00V)
used to approximate electric potentials
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| strongest oxidizing agent when comparing reduction potentials | this would be the one w/ the higher (more positive) reduction potential - more spontaneously reduced
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| strongest reducing agent when comparing reduction potentials | this would be the one w/ the more negative reduction potential - more spontaneously oxidized
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| 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
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| 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*
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| simple galvanic cell composed of.. | 2 electrodes - anode and cathode
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| anode in a galvanic cell | where the oxidation half rxn takes place
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| cathode in a galvanic cell | where the reduction half rxn takes place
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| electromotive force | (emf) aka cell potential, potential difference btw the terminals when they are not connected
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| standard state cell potential | sum of the standard state potentials of the corresponding half reactions
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| 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
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| terminal | electronic conductors (often metal wires), symbolized as T
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| 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)
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| 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
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| 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
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| positive cell potential indicates ___ free energy | negative
meaning rxn is spontaneous
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| free energy relating to reaction quotient eqn | delta(G) = delta(Go) + RTln(Q)
where Q = Products/Reactants
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| standard free energy eqn (relating to equilibrium constant) | delta(Go) = -RTln(K)
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| 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
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| Nernst eqn | E = Eo - (RT/nF)ln(Q)
expresses the relationship btw chemical concentrations and potential difference
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| 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
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| 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
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| 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
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