12. Electrochem Flashcards
Is anode/cathode red/ox?
anode = where oxidized, cathode = where reduced ALWAYS regardless of galvanic/voltaic or electrolytic cell
voltaic/galvanic cell vs electrolytic cell vs concentration cell vs rechargeable cell/battery
use spontaneous redox rxn to produce a current, anode = neg terminal & cathode = pos terminal vs use a current to produce a nonspontaneous redox rxn, anode = pos terminal & cathode = neg terminal vs type of galvanic cell that has 2 identical electrodes w/ diff conc: lower conc needs to be [O] and higher conc needs to be [H], it’s a spontaneous rxn vs act as both galvanic and electrolytic cell
Describe e- flow and ion flow b/w anode and cathode for non/spontaneous redox rxns
e- flow from anode to cathode for either cell; only the positions b/w anode and cathode changes (ie. spont: anode on left & neg and cathode right & pos vs nonspont: anode right & pos and cathode left & neg, BUT [O] and [H] still occur at their same respective nodes)
Cations of salt bridge = attracted to cathode, anions of salt bridge = attracted to anode
Know how to draw voltaic cell and electrolytic cell
voltaic: both electrodes (anode = neg terminal, cathode = pos terminal), current, and salt bridge
electrolytic: both electrodes (anode = pos, cathode = neg), current, salt bridge and battery on current (left side of battery = neg, right side of battery = pos)
Where do e- come from in electrolytic cell? Why do e- flow in opposite directions?
e- come from neg terminal of battery, e- from right anode becomes attracted to pos terminal of battery –> e- flow from right to left
What’s Faraday’s constant?
96500 C/1 mol e- or 1.602E-19 C/1 e-
Understand short hand of galvanic cells
anode | aq form || aq form | cathode
| = phase boundary, || = salt bridge
What does pos cell potential (E0 cell) aka emf mean? When looking up E0 reduction potential, what should you keep in mind?
Pos value means spontaneous rxn
E0 values = representative of reduction rxns; if you look for [O] rxns –> take opposite sign. As you look up the reduction potentials, the more oxidizing agents (ie. Will be reduced); as you look down the reduction potentials, the more reducing agents (ie. Will be oxidized)
Intensive property vs extensive property + examples
doesn’t matter how much you need, it’ll stay the same (ex. voltage) vs value changes depending on how much you need (ex. deltaG0)
What’s the diagonal rule?
any oxidizing agent can oxidize a reducing agent that’s below it on the standard reduction potential table. Side note: oxidizing agent cannot oxidize a reducing agent that’s above it on the same table
Know formula b/w deltaG0 and E0 cell potential
deltaG0 = -nFE0, where n = mol e- exchanged
E0 = E0red, cathode - E0red, anode
What does the 0 (degree sign) mean?
Standard conditions: 1 M slns, 25 degrees C, pure solids
What’s the Nernst eqn? How does it help you?
E = E0 - (0.0592V/n)logQ; helps you find E in nonstandard conditions
Can also be E = E0 - (0.0257/n)lnQ. Q = [prod]/[react]
What happens to E0 at equil?
Q = K, E0 = 0 –> cell = dead since rxn reached equil
Which cell drives spont and nonspont rxns?
Galvanic for spont, electrolytic (electrolysis) for nonspont
What should the solvent do in an electric cell?
Dissolve ions
When you multiply e- by a factor to make em match in redox rxns, do you need to multiply the corresponding voltage too?
Nah cuz it’s an intensive property (it stays the same no matter the conc)
Energy density
Measure of battery’s ability to produce power as a function of its weight; energy to weight ratio. Lead acid batteries require a heavier amount of matters material to produce a certain output (ie. Lowest energy density)
Cd-Ni batteries have higher e- density than lead acid batteries —> higher surge current - periods of large current early in discharge cycle
Lead acid battery vs Cd-Ni battery
Pb anode, PbO2 cathode, both coated with sulfuric acid, lowest energy density b/c need a lot of weight to produce energy vs cadmium anode, nickel cathode, both connected by conductive material (ex: KOH), higher energy density —> higher surge current
How to change EMF?
Change identity of electrode, not the amount; change temp too (this is basically like the equil constants)
How are strengths of electrolytes and their solubility in water relate? What does adding an electrolyte do?
stronger electrolytes can dissolve into more ions —> more conductivity. (Ex: strong acids and salts = strong electrolytes, weak acids = weak electrolytes). Electrolytes prevent charge buildup and inc conductivity in electrolysis; electrolytes should not be [O] or [H]
Electrodeposition eqn and how does it help you?
Find mol of metal deposited on a plate: mol Metal = (It)/(nF) where I = current, t = time, n = # of e- equiv, and F = faraday’s constant
mol of metal: It is Not Fun
