General Chemistry Chapter 12: Electrochemistry

Question 1

Electrochemical cell

Answer 1

describes 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 the site of oxidation. It attracts anions

Question 4

Cathode

Answer 4

always the side of reduction. It attracts cations.

Question 5

Electrons flow

Answer 5

from the anode to the cathode

Question 6

Current flows

Answer 6

from the cathode to the anode

Question 7

Cell diagrams

Answer 7

are shorthand notation that represent the reactions taking place in an electrochemical cell.

Question 8

Cell diagrams are written

Answer 8

from anode to cathode with electrolytes (the solution) in between.

Question 9

A vertical line represents

Answer 9

a phase boundary

Question 10

A double vertical line represents

Answer 10

a salt bridge or other physical boundary

Question 11

Galvanic (voltaic) cells

Answer 11

have spontaneous reactions (delta G

Question 12

Electrolytic cells

Answer 12

house nonspontaneous reactions (delta G > 0). They can be used to create useful products through electrolysis.

Question 13

Concentration cells

Answer 13

Are 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.

Question 14

Charge on an electrode for galvanic cells

Answer 14

Anode is negatively charged and the cathode is positively charged

Question 15

Charge on an electrode for electrolytic cells

Answer 15

Anode is positively charged and the cathode is negatively charged

Question 16

Rechargeable batteries

Answer 16

electrochemical cells that can experience charging (electrolytic) and discharging (galvanic) states. Often ranked by energy density - the amount of energy a cell can produce relative to the mass of battery material.

Question 17

Lead-acid batteries

Answer 17

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 restonre the original Pb and PbO2 electrodes and concentrate the electrolyte. Have low energy density.

Question 18

Nickel-cadmium batteries

Answer 18

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 electrodes and concentrate the electrolyte. These cells have a higher energy density than lead-acid batteries.

Question 19

Nickel-metal hydride (NiMH)

Answer 19

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

Question 20

Surge current

Answer 20

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

Question 21

Reduction potential

Answer 21

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 22

Standard reduction potentials (E’red)

Answer 22

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

Question 23

Standard electromotive force (Ecell)

Answer 23

the difference in standard reduction potential between the two half-cells.

Question 24

For galvanic cells, the difference of the reduction potentials of the two half reactions = ____
For electrolytic = ___

Answer 24

galvanic = positive
electrolytic = negative

Question 25

Relationship between E cell and Delta G

Answer 25

always have opposite signs

Question 26

Ecell and Delta G in galvanic cells

Answer 26

E = + and G = -

Question 27

Ecell and Delta G in electrolytic cells

Answer 27

negative

Question 28

In concentration cells, Ecell and Delta G

Answer 28

both = 0

Question 29

Nernst equation

Answer 29

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

Question 30

When Keq is greater than 1, Ecell

Answer 30

is +

Question 31

When Keq is less than 1, Ecell

Answer 31

is -

Question 32

When Keq is equal to 1, Ecell

Answer 32

is 0