electrochemistry

Question 1

electrochemistry real world applications

Answer 1

photosynthesis, conversion of food to energy, combustion, batteries and fuel cells, corrosion and prevention

Question 2

What is being reduced and oxidized? 2Fe 3+ + HCO2H + 2H2O –> 2Fe2+ + CO2 + 2H30+

Question 3

rules for balancing redox rxns

Answer 3

1. separate into 2 half rxns
2. balance all elements except O and H
3. Balance O with H2O
4. balance H with H+
5. Balance charge with e-
6. Find multiplier that allows e- to cancel
7. combine/add half rxn together
8. check to be sure balaced- this is for acidic conditions
9. for basic conditions, add OH- to both sides to eliminate H+, cancel residual water, check again

Question 4

practice C2O4 2- + MnO4- <–> CO2 + Mn2+

Question 5

galvanic electrochem cell beaker sketch: Fe (s) –> Fe2+ + 2e- , Cu2+ + 2e- –> Cu (s)

Question 6

Standard Hydrogen Electrode (SHE) 2H+ 9aq) + 2e- –. H2(g) purpose

Answer 6

a standard to compare the reaction potential of all other substances

Question 7

cell potentials

Answer 7

electrochemical cells generate electricity (e- flow) by physically separating two half rxns, each half cell contributes to overall cell potential (voltage cell can produce)

Question 8

E° cell equation

Answer 8

E°cell= E°oxidation + E°reduction OR E°cell= E°cathode- E°anode

Question 9

Standard reduction potentials

Answer 9

always given in reduction format, use to find oxidation potential by multiplying by (-) flipping rxn

Question 10

manipulating E° potentials

Answer 10

• flip sign when E°red becomes E°ox
• if multip;y rxn by constant DO NOT multiply E°red- intensive property

Question 11

galvanic cell overview

Answer 11

-balanced redox rxn for an electrochemical cell
- designate cathode and anode
-SRP to determine the direction of e- flow, calculate E° cell for system
for galvanic cell E°cell should be (+) and spontaneous
- consider phases for all species involved, may need chemically inert conductor Pt or graphite as electrode for non-solid species like H2 (g) specify in diagram

Question 12

1 coulomb (C)

Answer 12

Measure of charge on 6.2x10^18 e-

Question 13

charge on 1 e-

Answer 13

1.6x10^-19 C

Question 14

1 Faraday (F)

Answer 14

charge on 1 mol e- = 96,485 C/mol e-

Question 15

1 Volt (V) = 1 Joule per Coulomb = 1 J/C

Question 16

Half-reactions are defined by changes in free energy associated with transferring e-

Answer 16

since half rxn potential is determined by free energy change from electron transfer, we can find the free energy delta G carried by 1 Coulomb charge – this is SRP for half rxn

Question 17

relationship between E and delta G

Answer 17

E has opposite sign as delta G

Question 18

if energy is released (delta G> 0) then

Answer 18

electrons will be carried through cell, positive E potential

Question 19

role of Q

Answer 19

accounting for concentrations and pressures that are not standard state

Question 20

Q, K, and delta G at at equilibrium

Answer 20

Q=K, Delta G= 0

Question 21

when not at EQ, cell potential shifts

Answer 21

left or right, depending on cell potential

Question 22

nernst equation

Answer 22

Delta G°= -nFE° – see eq sheet for more examples of derivatives

Question 23

spontaneous forward direction

Answer 23

delta G° <0, E° cell>0, K >1

Question 24

spontaneous in the reverse direction

Answer 24

delta G° >0, E° cell<0, K <1

Question 25

no net rxn: system at eq

Answer 25

delta G° 0, E° cell 0, K 1

Question 26

what will happen to cell with identical electrodes and different ion concentrations, how will sys shift to reach eq

Question 27

primary batteries

Answer 27

high power, long-lasting, inexpensive, NON-rechargeable (single use) ex: dry cell battery

Question 28

secondary batteries

Answer 28

rechargeable for many cycles, ex: lead acid battery, lithium-ion battery

Question 29

fuel cells

Answer 29

"clean" run on hydrogen-containing fuel, longer lifetime than traditional batteries, ex: Proton Exchange Membrane

Question 30

corrosion

Answer 30

spontaneous, undesirable redox chemistry

Question 31

corrosion prevention

Answer 31

1. protective later (paint) 2. mix in corrosion-resistant metals (alloy to protect vulnerable material with corrosion-resistant species) 3. Physically connect the sacrificial anode (donate e- to the system first, protecting another metal from unwanted oxidation (more negative SRP, ex: zinc, mg)

Question 32

electrolysis definition

Answer 32

Reverse of galvanic cell: input a voltage to run the electrochemical rxn in non-spontaneous rxn

Question 33

electrolysis applications

Answer 33

- can be used to selectively "plate out" metals that are dissolved in solution - industrial processes such as aluminum and copper refinement

Question 34

faraday's law of electrolysis

Answer 34

n=It/F

Question 35

Electrolysis practice problem

Answer 35

check discussion worksheet

Question 36

sketch galvanic cell

Answer 36

galvanic cell characteristics: - spontaneous - chemical energy turns into electrical energy - wide range anode/cathode combinations possible - cell potential determined from E red of half cells often two diff half rxns

Question 37

sketch concentration cell

Answer 37

concentration cell characteristics: - type of galvanic call - same half rxn in cathode and anode e - different concentrations drive cell towards equilibrium (equal concentration)

Question 38

sketch electrolytic cell

Answer 38

Electrolytic cell characteristics: - non-spontaneous - electrical energy turns into chemical energy - powered with current - metal ions from solution (or other products) form at electrode -some similarities to cathode of galvanic cell - E red determines which product forms if multiple possible