12. Electrochem

Question 1

Is anode/cathode red/ox?

Answer 1

anode = where oxidized, cathode = where reduced ALWAYS regardless of galvanic/voltaic or electrolytic cell

Question 2

voltaic/galvanic cell vs electrolytic cell vs concentration cell vs rechargeable cell/battery

Answer 2

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

Question 3

Describe e- flow and ion flow b/w anode and cathode for non/spontaneous redox rxns

Answer 3

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

Question 4

Know how to draw voltaic cell and electrolytic cell

Answer 4

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)

Question 5

Where do e- come from in electrolytic cell? Why do e- flow in opposite directions?

Answer 5

e- come from neg terminal of battery, e- from right anode becomes attracted to pos terminal of battery –> e- flow from right to left

Question 6

What’s Faraday’s constant?

Answer 6

96500 C/1 mol e- or 1.602E-19 C/1 e-

Question 7

Understand short hand of galvanic cells

Answer 7

anode | aq form || aq form | cathode

| = phase boundary, || = salt bridge

Question 8

What does pos cell potential (E0 cell) aka emf mean? When looking up E0 reduction potential, what should you keep in mind?

Answer 8

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)

Question 9

Intensive property vs extensive property + examples

Answer 9

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)

Question 10

What’s the diagonal rule?

Answer 10

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

Question 11

Know formula b/w deltaG0 and E0 cell potential

Answer 11

deltaG0 = -nFE0, where n = mol e- exchanged

E0 = E0red, cathode - E0red, anode

Question 12

What does the 0 (degree sign) mean?

Answer 12

Standard conditions: 1 M slns, 25 degrees C, pure solids

Question 13

What’s the Nernst eqn? How does it help you?

Answer 13

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]

Question 14

What happens to E0 at equil?

Answer 14

Q = K, E0 = 0 –> cell = dead since rxn reached equil

Question 15

Which cell drives spont and nonspont rxns?

Answer 15

Galvanic for spont, electrolytic (electrolysis) for nonspont

Question 16

What should the solvent do in an electric cell?

Answer 16

Dissolve ions

Question 17

When you multiply e- by a factor to make em match in redox rxns, do you need to multiply the corresponding voltage too?

Answer 17

Nah cuz it’s an intensive property (it stays the same no matter the conc)

Question 18

Energy density

Answer 18

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

Question 19

Lead acid battery vs Cd-Ni battery

Answer 19

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

Question 20

How to change EMF?

Answer 20

Change identity of electrode, not the amount; change temp too (this is basically like the equil constants)

Question 21

How are strengths of electrolytes and their solubility in water relate? What does adding an electrolyte do?

Answer 21

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]

Question 22

Electrodeposition eqn and how does it help you?

Answer 22

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