Chemistry Chapter 8: Redox Reactions and Electrochemistry

Question 1

A concentration cell is a type of

Answer 1

galvanic cell

Question 2

Definition of oxidation state

Answer 2

The oxidation state of an atom is a hypothetical charge it would have if all bonds were considered to be 100% ionic.

Measure of electron distribution in a chemical species

Question 3

Pure element’s oxidation state:

Answer 3

0

Question 4

Monoatomic ions oxidation state:

Answer 4

Same as charge. Ie Fe2+ is +2

Question 5

Sum of oxidation states

Answer 5

= charge of molecule

Question 6

Oxidation state of fluorine

Answer 6

-1

Question 7

Oxidation state of halogens

Answer 7

-1 unless bonded to more electronegative halogen or N or O (could be +1, 3, 5, 7)

Question 8

Standard Reduction Potential

Answer 8

Measure of how much a species likes to be REDUCED. The standard cell potential is the potential difference between the cathode and anode.

Measured in volts

E°

Question 9

All standard reduction potentials are measured relative to the

Answer 9

hydrogen electrode (0V)

Question 10

The more positive the reduction potential

Answer 10

the more the species likes to be reduced (spontaneous)

Question 11

the more negative the reduction potential

Answer 11

the more the species doesn’t to be reduced (nonspontaneous)

Question 12

which species will be reduced and which will be oxidized? What do you do to the oxidized species?

Answer 12

These are reduction potentials so Ag will be reduced.

Make sure to reverse the oxidized species

Question 13

Do you need to balance reduction and oxidization potentials?

Answer 13

NO. Reduction and oxidization potentials are not affected by stiochiometric constants. IE if you double the products, you still get the same voltages for reduction potential

Question 14

What reaction takes place at the cathode? (regardless if it’s a galvanic or electrolytic cell)

Answer 14

Reduction

red cat

Question 15

What reaction takes place at the anode? (regardless if it’s a galvanic or electrolytic cell)

Answer 15

oxidation

an ox

Question 16

Galvanic Cell

Answer 16

spontaneous reduction reaction is used to generate a POSITIVE potential difference that drives a current

Question 17

In galvanic cells, E°cell must always be

Answer 17

POSITIVE because spontaneous

Question 18

How to find reaction direction in a galvanic cell

Answer 18

Method 1: Determine reaction at cathode and anode. Reverse the half-reaction at the anode and flip RP sign. Add potentials.

Method 2: use E°cell = E°cathode - E°anode (USE ONLY REDUCTION potentials)

Question 19

Daniell Cell - why does it have a salt bridge?

Answer 19

common set up for a galvanic cell

the anode comes more positive and the cathode becomes more negative

so this charge imbalance would grow that electrons are repelled from cathode and therefore reaction would stop

Question 20

what does this shorthand mean

Answer 20

Question 21

Concentration Cell conditions

Answer 21

1) Electrodes must be the same material
2) two regions must have concentration difference

type of galvanic cell

Question 22

Electrolytic cell

Answer 22

Electrical energy is used to drive nonspontaneous redox reactions

Question 23

Electrolytic cells always have __________ E°cell values

Answer 23

NEGATIVE because they are non spontaneous

Question 24

true or false

Electrodes in electrolytic cells are conductive but won’t engage in unwanted side reactions

Answer 24

true

Question 25

Cathode in electrolytic cell is (positive/negative?)

Answer 25

negative

Question 26

Anode in electrolytic cell is (positive/negative?)

Answer 26

Positive

Question 27

Regardless of cell type, electrons always move from

Answer 27

Anode to Cathode

Question 28

Electroplating

Answer 28

Nonspontaneous reduction of metal ions in solution. Results in deposition of solid metal onto the cathode

Question 29

Equation for mols of metal plated

Answer 29

n = mol e- transferred and F = Faraday's constant = 1 x 10^5C/mol e-. remember that Current can also be thought of as C/s

Question 30

When a battery is discharging it's acting as a

Answer 30

galvanic cell

Question 31

When a battery is charging it's acting as a

Answer 31

electrolytic cell

Question 32

Examples of rechargeable batteries

Answer 32

Lead Acid and Nickel Cadmium

Question 33

Why use the nernst equation?

Answer 33

helps account for how electrical potential of a cell is affected by temperature and concentration of reactions

Question 34

what is the nernst equation

Answer 34

The Nernst equation is used to calculate the electrode potential (E) of an electrochemical cell under non-standard conditions, where ion concentrations are different from 1 M and/or the temperature is not 25°C.

Question 35

Under standard conditions (25C) how can you simplify the nernst equation?

Answer 35

Question 36

Calculating free energy of a redox reaction in an electrochemical cell

Answer 36

Question 37

If delta G is't given, what do you do for chemical cells

Answer 37

Question 38

Spontaneous reaction has what delta G, Ecell and Keq?

Answer 38

Question 39

Non-spontaneous reaction has what delta G, Ecell and Keq?

Answer 39

Question 40

How to solve this question

Answer 40

1) figure out what is oxidized and what is reduced at the anode/cathode for a galvanic cell. IE Ni2+ +2e- --> Ni is reduced at the cathode 2) REVERSE this for the electrolytic cell (recharging). ie Cd2+ + 2e- --> Cd is reduced at the cathode. Therefore, Cd is deposited at the cathode

Question 41

Do you need a salt bridge for an electrolytic cell?

Answer 41

NO In an electrolytic cell, an external power source drives the reaction non-spontaneously. Since the external voltage forces electrons to move, there's no need for a salt bridge to maintain charge neutrality. Instead, ions in the same electrolyte solution (or sometimes a porous membrane) help complete the circuit.

Question 42

Why do you need a salt bridge for galvanic cells?

Answer 42

Because there is a build up of negative charge on the cathode (since the electrons flow from anode to cathode). the circuit grinds to a halt if there's a build up negative charge because cathode becomes LESS positive (and we need therefore the salt bridge lets positive ions to travel to the cathode to balance out negative charge

Question 43

Difference between which charge to follow for circuits vs chemical cells

Answer 43

Follow electrons for chemical reactions. In galvanic cells, electrons flow from the negative anode to the positive cathode. Follow current (positive charge) for circuits. Conventional current flows from the positive cathode to the negative anode.

Question 44

When NAD+ gets reduced, why does a H+ get added (since H+ is positive)

Answer 44

NAD+ gains 2 electrons (from oxidized species)