Chapter 12 Electrochemistry

Question 1

What are the 4 things all electrochemical cells have?

Answer 1

• Anode is always the site of oxidation. It attracts anions.
• Cathode is always the site of reduction. It attracts cations.
• Electrons flow from the anode to the cathode.
• Current flows from the cathode to the anode.

Question 2

What is shorthand notation for electrochemical cells?

Answer 2

• Written from anode to cathode
• vertical line = phase boundary
• double vertical line = salt bridge or other physical boundary

Question 3

Difference between Galvanic and Electrolytic cells?

Answer 3

Galvanic has spontaneous rxns (ΔG < 0) with a positive electromotive force.

Electrolytic has nonspontaneous (force required) reactions (ΔG> 0) with a negative electromotive force. *Can do electrolysis

Question 4

What is the electromotive force (emf)?

Answer 4

Corresponds to the voltage or electrical potential difference of
the cell

Question 5

What are concentration cells?

Answer 5

Type of galvanic cell in which
both electrodes are made of the same material. potential Not potential difference but concentration gradient causing movement.

Question 6

What are the charges on galvanic and electrolytic cells?

Answer 6

Galvanic: (-) Anode, (+) Cathode

Electrolytic Cells: (-) Cathode, (+) Anode

Question 7

What is energy density?

Answer 7

Energy produced relative to mass

Question 8

What is a Lead-acid battery?

Answer 8

• Pb anode and a PbO2 cathode in a sulfuric acid solution.
• Low energy density

Question 9

What is Nickel–cadmium battery?

Answer 9

• Cd anode and a NiO(OH) cathode in KOH solution.
• higher energy density than lead–acid batteries

Question 10

What is a Nickel–metal hydride (NiMH) battery?

Answer 10

More or less replaced Ni–Cd batteries b/c they have higher energy density, are more cost effective, and are significantly less toxic.

Question 11

What is a surge current?

Answer 11

High current at the beginning of discharge that wanes till stable

Question 12

What is reduction potential?

Answer 12

how likely a compound is to be
reduced. The more positive the value, the more likely it is to be reduced

• Measured under standard conditions (298K)

Question 13

What is the standard electromotive force?

Answer 13

• the difference in standard
  reduction potential between the two half-cells.
• For galvanic cells, the difference of the reduction potentials of the two half-reactions is positive; for electrolytic cells, the difference of the
  reduction potentials of the two half-reactions is negative.

Question 14

What is the relationship between Electromotive force and change in free energy?

Answer 14

Always have opposite signs.

• When E° cell is positive, ΔG° is negative. This is the case in galvanic cells.
• When E° cell is negative, ΔG° is positive. This is the case in electrolytic cells.
• When E° cell is 0, ΔG° is 0. This is the case in concentration cells.

Question 15

What does the Nernst equation describe?

Answer 15

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

Question 16

What is the relationship between Keq and E° cell?

Answer 16

• Keq > 1, E° cell is positive, products are favored
• Keq < 1, E° cell is negative
• Keq =1, E° cell is 0.

Question 17

What is the point of the salt bridge?

Answer 17

exchange anions and cations to balance, or dissipate, newly generated charges.

Question 18

What is one Faraday?

Answer 18

equivalent to the amount of charge contained in one mole of electrons (1 F = 96,485 C)

Question 19

What is the electrodepostion equation?

Answer 19

MNEMONIC: Calculating Moles of Metal, It is Not Fun.

mol M = It/nF