Ch 12: Electrochemistry

Question 1

electrochemical cell

Answer 1

any cell in which oxidation-reduction reactions take place. Certain characteristics are shared between all types of electrochemical cells

Question 2

Electrodes

Answer 2

strips of metal or other conductive materials placed in an electrolyte solution

Question 3

anode

Answer 3

always site of oxidation. it attracts anions

Question 4

cathode

Answer 4

always the site of reduction. it attracts cations

Question 5

electrons flow from ____ to ____

Answer 5

anodes

cathodes

Question 6

current flows from ____ to ____

Answer 6

cathode

anode

Question 7

cell diagrams

Answer 7

shorthand notation that represents the reactions taking place in an electrochemical cell

Question 8

cell diagrams are written from anode to cathode with ____ in between

Answer 8

electrolytes (the solution)

Question 9

a vertical line represents a ____, and a double vertical line represents a ____ or other physical boundary

Answer 9

phase boundary

salt bridge

Question 10

galvanic (voltaic) cells

Answer 10

house spontaneous reactions (delta G

Question 11

electrolytic cells

Answer 11

house nonspontaneous reactions (delta G > 0) with a negative electromotive force. these nonspontaneous cells can be used to create useful products through electrolysis

Question 12

concentration cells

Answer 12

specialized form of 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 two solutions

Question 13

charge of an electrode is dependent on

Answer 13

type of electrochemical cell one is studying

for galvanic cells, anode is neg and cathode is pos
for electrolytic cells, anode is pos and cathode is neg

Question 14

rechargeable batteries

Answer 14

electrochemical cells that experience charging (electrolytic) and discharging (galvanic) states

often ranked by energy density, the amount of energy a cell produces relative to the mass of battery material

Question 15

lead-acid batteries

Answer 15

when discharging consist of a 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

Question 16

nickel-cadmium batteries (Ni-Cd)

Answer 16

when discharging consist of a Cd anode and a NiO(OH) cathode in a concentrated KOH solution

when charging, Ni(OH)2- and Cd(OH)2- plated electrodes are dissociated to restore the original Cd and NiO(OH) electrodes and concentrate the electrolyte. these cells have a higher energy density than lead-acid batteries

Question 17

nickel-metal hydride (NiMH)

Answer 17

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

Question 18

surge current

Answer 18

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

Question 19

reduction potential

Answer 19

quantifies the tendency for a species to gain electrons and be reduced. the higher the reduction potential, the more a given species wants to be reduced.

Question 20

standard reduction potentials (Enot,red) are calculated by comparison to the ____ under standard conditions ____

Answer 20

standard hydrogen electrode (SHE)

298K, 1 atm pressure, 1 M concentrations

Question 21

standard hydrogen electrode has a standard reduction potential of

Answer 21

0V

Question 22

Standard electromotive force (Eknot, cell)

Answer 22

difference in standard reduction potential between the two half-cells

Question 23

for galvanic cells, the difference of the reduction potentials of the two half-reactions is ____; for electrolytic cells, the difference of the reduction potentials of the _____ is negative

Answer 23

positive

two half-reactions

Question 24

electromotive force and ____ always have opposite signs

Answer 24

change in free energy

Question 25

when Eknot,cell is positive, delta G is

Answer 25

negative. This is a galvanic cell

Question 26

When Eknot,cell is negative, delta G is

Answer 26

positive. This is the case in a electrolytic cell

Question 27

When Eknot,cell is 0, delta Gknot is

Answer 27

0 this is case in concentration cells

Question 28

nernst equation

Answer 28

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

Question 29

there is a relationship between Keq (equilibrium constant) and

Answer 29

Eknot,cell

Question 30

When Keq (ratio of products conc at equilibrium / reactants all raised to their stoichiometric coefficients) > 1

Answer 30

Ecell is positive

Question 31

Keq

Answer 31

negative

Question 32

When Keq = 1 then Ecell is

Answer 32

0