Electrochemistry

Question 1

describes any cell in which oxidation-reduction reactions take place; three types: galvanic, electrolytic, and concentration cells; all types share certain characteristics

Answer 1

electrochemical cells

Question 2

strips of metal or other conductive material placed in an electrolytic solution

Answer 2

electrodes

Question 3

electrodes:

always the site of oxidation; it attracts anions

Answer 3

anode

Question 4

electrodes:

always the site of reduction; it attracts cations

Answer 4

cathode

Question 5

electrode mnemonic

Answer 5

AN OX and a RED CAT

Question 6

electrodes:

flows from the anode to the cathode

Answer 6

electrons

Question 7

electrodes:

flows from the cathode to the anode

Answer 7

current

Question 8

shorthand notation that represents the reactions taking place in an electrochemical cell; written from anode to cathode with electrolytes (the solution) in between; a vertical line represents the phase boundary, and a double vertical line represents a salt bridge or other physical boundary
e.g. Zn (s) | Zn2+ (1 M) || CU2+ (1 M) | Cu (s)

Answer 8

cell diagrams

Question 9

cell diagram form:

Answer 9

anode | anode solution (concentration) || cathode solution (concentration) | cathode

Question 10

house spontaneous reactions (∆G < 0) with a positive electromotive force; anode is negatively charged and cathode is positively charged

Answer 10

galvanic (voltaic) cells

Question 11

house nonspontaneous reactions (∆G > 0) with a negative electromotive force; these negative nonspontaneous cells can be used to create useful products through electrolysis; anode is positively charged and cathode is negatively charged

Answer 11

electrolytic cells

Question 12

a specialized form of a galvanic cell in which both electrodes are made of the same material; rather than a potential difference causing the movement of charge, it is the concentration gradient between the two solutions

Answer 12

concentration cells

Question 13

electrochemical cells that can experience charging (electrolytic) and discharging (galvanic) states; often ranked by energy density

Answer 13

rechargeable batteries

Question 14

rechargeable batteries:

the amount of energy a cell can produce relative to the mass of the battery material

Answer 14

energy density

Question 15

rechargeable batteries:
when discharging, consist of Pb anode and a PbO2 cathode in a concentrated sulfuric acid solution; when charging, the PbSO4 plated electrodes are dissociated to restore the original Pb and PbO2 electrodes and concentrate the electrolyte; these cells have low energy density

Answer 15

lead-acid batteries

Question 16

rechargeable batteries:
when discharging, consist of a Cd anode and a NiO(OH) cathode in a concentrated KOH solution; when charging, the Ni(OH)2 and Cd(OH)2 plated electrodes are dissociated to restore the original Cd and NiO(OH) electrodes and concentrate the electrolyte; theses cells have a higher energy density than lead-acid batteries

Answer 16

nickel-cadmium batteries (Ni-Cd)

Question 17

rechargeable batteries:
have more or less replaced Ni-Cd batteries because they have higher energy density, are more cost effective, and are significantly less toxic

Answer 17

nickel-metal hydride batteries (NiMH)

Question 18

an above-average current transiently released at the beginning of the discharge phase; it wanes rapidly until a stable current is achieved

Answer 18

surge current

Question 19

quantifies the tendency for a species to gain electrons and be reduced; the higher the ____, the more a given species wants to be ____

Answer 19

reduction potential (reduced)

Question 20

are calculated by comparison to the standard hydrogen electrode (SHE) under the standard conditions of 298 K, 1 atm, and 1 M

Answer 20

standard reduction potentials (Eº(red))

Question 21

has a standard reduction potential of 0 V

Answer 21

standard hydrogen electrode (SHE)

Question 22

the difference in standard reduction potential between two half-cells

Answer 22

standard electromotive force (Eº(cell))

Question 23

positive for galvanic cells, and negative for electrolytic cells

Answer 23

standard electromotive force (Eº(cell))

Question 24

always have opposite signs

Answer 24

electromotive force and change in free energy

Question 25

describes the relationship between the concentration of species in a solution under nonstandard conditions and the electromotive force

Answer 25

Nernst equation

Question 26

Nernst equation

Answer 26

E(cell) = Eº(cell) - (.0592 / n) log Q

where:
E(cell) = emf of cell under nonstandard conditions
Eº(cell) = emf of cell under standard conditions
n = number of moles of electrons
Q = reaction quotient

Question 27

relationship between K(eq) and Eº(cell):
if K(eq) > 1

Answer 27

Eº(cell) is positive

Question 28

relationship between K(eq) and Eº(cell):
if K(eq) < 1

Answer 28

Eº(cell) is negative

Question 29

relationship between K(eq) and Eº(cell):
if K(eq) = 1

Answer 29

Eº(cell) is 0