Ch. 12: Electrochemistry

Question 1

Electrochemical Cell

Answer 1

Describes any cell in which oxidation reduction rxns 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 site of reduction. It attracts cations

Question 5

Electron flow and current flow

Answer 5

Electrons flow from anode to cathode; current flows from the cathode to the anode

Question 6

Cell Diagrams

Answer 6

Shorthand notation that represent the reactions taking place in an electrochemical cell

• Written from anode to cathode w electrolytes (the solution) in between
• A vertical line represents a phase boundary, and a double vertical line represents a salt bridge or other physical boundary

Question 7

Galvanic (voltaic) cells

Answer 7

House spontaneous rxns (🔼G<0) w a positive electromotive force

Question 8

Electrolytic Cells

Answer 8

House nonspontaneous rxns (🔼G>0) w a negative electromotive force. Can be used to create useful products through electrolysis

Question 9

Concentration cells

Answer 9

Specialized from of a galvanic cell in which both electrodes are made of the same material. Rather than a potential diff causing the movement of charge, it is the concentration gradient between the two solutions

Question 10

Charge on an electrode

Answer 10

Dependent on the type of electrochemical cell

• galvanic: anode = negative charge; cathode = positive charge
• electrolytic cels: anode = positive charge; cathode = negative charge

Question 11

Rechargeable batteries:

Answer 11

Electrochemical cells that can experience charging (electrolytic) and discharging (galvanic) states. Rechargeable batteries are often ranked by energy density

Question 12

Energy Density

Answer 12

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

Question 13

Lead-acid batteries

Answer 13

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 14

Nickel-Cadmium Batteries

Answer 14

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. These cells have a higher energy density than lead-acid batteries

Question 15

Nickel-metal hydride (NiMH) batteries

Answer 15

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

Question 16

Surge Current

Answer 16

Above average current transiently released at the begining of the discharge phase; it wanes rapidly until a stable current is achieved

Question 17

Reduction potential

Answer 17

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

Question 18

Standard Reduction Potentials (Ered)

Answer 18

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

Question 19

Standard Hydrogen electrode

Answer 19

Has a standard reduction potential of 0 V

Question 20

Standard electromotive force

Answer 20

E*cell; diff in standard reduction potential between the two half cells

Question 21

Difference of Half rxn reduction potentials

Answer 21

For galvanic cells, the diff of the reduction potential of the two half reactions is positive; for electrolytic cells, the diff of the reduction potentials of the 2 half-reactions is negative

Question 22

Electromotice force and change in free energy…

Answer 22

Always have opposite signs”

• when E*cell is positive, 🔼G is negative, this is the case in galvanic cells
• when E*cell is negative, 🔼G is positive, this is the case in electrolytic cells
• when E*cell is 0, 🔼G is 0, this is the case in concentration cells

Question 23

Nernst equation

Answer 23

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

Question 24

Relationship between equilibrium constant Keq and E*cell

Answer 24

• when Keq (the ratio of products’ concentrations at equilibrium over reactants’, raised to their stoichiometric coefficients) is greater than 1, E*cell is positive
• when Keq is less than 1, E*cell is negative
• when Keq is equal to 1, E*cell is )