Chapter 4: 4.2 Voltaic Cells

Question 1

Define:

Electrochemistry

Answer 1

The branch of chemistry that studies this interconversion of chemical and electrical energy

Question 2

Define:

Electrochemical cells

Answer 2

The experimental setup that produces or uses an electric current and does or converts electrical work through the use of a redox reaction

Question 3

Define:

Galvanic cells/Voltaic cell

Answer 3

Electrochemical cells that produce current

Question 4

Define:

Electrolysis

Answer 4

The process if a chemical reaction is forced to occur in an electrochemical cell by introducing an electric current from an external source

Question 5

Define:

Electrolytic cell

Answer 5

When the experimental setup,

Question 6

Define:

Half-cell

Answer 6

The physically separated subsystem where each half reaction occurs

Question 7

Where in each half-cell do the half-reactions take place?

Answer 7

On the surfaces of an electrode

Question 8

Define:

Electrode

Answer 8

An electronic conductor (usually a metal or graphite bar) that is in contact with an ionic conductor or electrolyte

Question 9

What is usually used as an electrolyte?

Answer 9

A solution or a molten salt

Question 10

How was the battery built by Volta?

Answer 10

Used a stacked pile of alternating zinc and copper disks separated by cloth soaked in brine and sulfuric acid

Question 11

What was the successor to Volta’s battery design?

Answer 11

The Daniell Cell

Question 12

True or False:

Reduction occurs at the cathode

Answer 12

True

Question 13

What does oxidation occur in a electrochemical cell?

Answer 13

Anode

Question 14

In a cell diagram:

What is written first on the left?

(Use Zn + Cu2+ → Zn2+ Cu)

Answer 14

The anode
* Zn

Question 15

In a cell diagram:

How is are the other species written?

(Use Zn + Cu2+ → Zn2+ Cu)

Answer 15

Written in the order in which they occur in the cell from the anode to the cathode
* Zn, Zn2+, Cu2+, Cu

Question 16

In a cell diagram:

What do vertical lines indicate?

(Use Zn + Cu2+ → Zn2+ Cu)

Answer 16

Phase boundaries
* Zn|Zn2+, Cu2+|Cu

Question 17

In a cell diagram:

What does a double vertical bar indicate?

(Use Zn + Cu2+ → Zn2+ Cu)

Answer 17

The salt bridge (or equivalent)
* Zn|Zn2+||Cu2+|Cu

Question 18

In a cell diagram:

What are inert electrodes? How are they indicated?

Answer 18

Graphite, platinum etc.
* Placed on the anode/cathode end as applicable
* Separated from the adjacent phase by single vertical bar

Question 19

True or False:

Stoichiometric coefficients are shown on cell diagrams

Answer 19

False, the following 2 are not shown on cell diagrams:
1. Stoichiometric coefficients
2. Species that are neither reduced nor oxidized

Question 20

1. What is the electrical energy difference (E)?
2. What is it also known as?
3. How can it be measured?

Answer 20

1. The electrical energy difference between any two electrodes in an electrochemical cell
2. Cell potential or cell voltage
3. Experimentally measured with a voltmeter

Question 21

What is standard conditions for electrochemical cells?

Answer 21

1.0 M and 25°C

Question 22

What is the standard potentials of electrodes measured relative to?

Answer 22

Standard hydrogen electrode (SHE)

Question 23

True or False:

Stronger oxidizing agents have more negative E^o values

Answer 23

False, they have more positive E^o values

Question 24

What E^o values are associated with stronger reducing agents?

Answer 24

Lower E^o values

Question 25

List:

The steps to finding the Standard Cell Potential

Answer 25

1. Identify the reduction half-reaction and look up its standard potential
2. Identify the oxidation half-reaction and look up its standard potential
3. Cell potential is the difference between the reduction half reaction potential minus oxidation half-reaction potential

Question 26

True or False:

When calculating standard cell potential, we multiply the E^o values by the coefficients required to cancel electron values

Answer 26

False, the E^o values is NOT multiplied

Question 27

How is the standard cell potential of a redox reaction related to that reaction’s standard free energy change?

Answer 27

ΔG^o = -nFE^o(cell)

Question 28

In the reaction ΔG^o = -nFE^o(cell):
1. What does n stand for?
2. What does F stand for?

Answer 28

1. Number of moles of electrons transferred between the electodes in the complete reaction
2. Proportionality constant (Faraday constant)

Question 29

What is the value of the Faraday constant?

Answer 29

96,485 Coulombs (C) per mole of unit charges

Question 30

How can we tell if a given redox reaction will occur spontaneously as written based on the sign of the corresponding standard cell potential?

Answer 30

1. If E^o(cell), then the reaction is spontaneous from left to right as written
2. If E^o(cell), then the reverse reaction (from right to left) is spontaneous
3. If E^o(cell), then the cell reaction is at equilibrium

Question 31

The relationship between free energy under non-standard and standard conditions is shown by which equation?

Answer 31

ΔG = ΔG^o +RTlnQ

Question 32

The relationship between free energy under standard and non-standard conditions using cell potentials will form a formula known as what?

Answer 32

Nernst Equation

Question 33

State the formula for:

Nernst Equation

Answer 33

E(cell) = E^o(cell) - (RT/nF)lnQ

Question 34

State:

The variables of the Nernst equation

Answer 34

E(cell) = E^o(cell) - (RT/nF)lnQ
* Q is the reaction quotient
* R is the gas constant = 8.314 J/K mol
* T is the absolute temperature in Kelvin