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Ek Chem 7
Electrochemistry
| Question | Answer |
|---|---|
| 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
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