Unit 5: Electrochemistry

Question 1

What is electrochemistry?

Answer 1

It is the study of the interchange of chemical energy and electrical energy.

Question 2

What is reduction?

Answer 2

Electron gain

Question 3

What is oxidation?

Answer 3

Electron loss

Question 4

What is oxidation state?

Answer 4

The charge the atom would have if all the ve- in the bonds are bonded.

Question 5

What is an oxidizing agent?

Answer 5

The species that is reduced.

Question 6

What is the reducing agent?

Answer 6

The species that is oxidized.

Question 7

What are the steps to predicting redox reactions?

Answer 7

1. List all possible reduction and oxidation species.
2. Determine the SRA and SOA
3. Write out the half reactions
4. Balance and combine half reactions

Question 8

What are the properties of a voltaic cell?

Answer 8

• Chem energy –> electrical energy
• Energy is released from a spontaneous redox reaction
• System does work on surroundings.

Question 9

What are the properties of an electrolytic cell?

Answer 9

• Electrical energy –> chem energy
• Energy is absorbed to drive a nonspontaneous redox reaction
• Surroundings (power supply) do work on the system (cell).

Question 10

What half reaction occurs at the cathode?

Answer 10

Reduction

Question 11

What reaction occurs at the anode?

Answer 11

Oxidation

Question 12

What are the two ways to create a voltaic cell?

Answer 12

1. Mix the chemicals in single compartments
2. Chemicals in separate compartments which are connected via a salt bridge

Question 13

Where do cations flow?

Answer 13

Towards the cathode.

Question 14

Whare do anions flow?

Answer 14

Towards the anode.

Question 15

What is cell potential?

Answer 15

The voltage difference between the two half cells.

Question 16

What is the set up of a cell diagram?

Answer 16

• Anode on the left
• Cathode on the right
• | = phase boundary
• || = salt bridge
• concentrations or pressure are given in ()
• Phase notation is omitted

Question 17

What happens if Ecell > 0?

Answer 17

• Ec > Ea
• The reaction is spontaneous

Question 18

What happens if Ecell < 0?

Answer 18

• Ec < Ea
• The reaction in nonspontaneous

Question 19

What is required for a redox reaction to be successful?

Answer 19

On the redox table the OA needs to be above the RA.

Question 20

What are the two methods for determining the spontaneity of a redox reaction?

Answer 20

1. Write the reactions as reductions and get E from the table.
2. Flip reactions to get an overall reaction.

Question 21

Is E multiplied by an integer?

Answer 21

No because the half cell potential is an intensive property.

Question 22

What is potential difference (V)?

Answer 22

V= w (work) / q (charge)

Question 23

What is charge (q)?

Answer 23

q = n (mols of e- transferred) F

Question 24

Does the work done by a system on the surroundings have a + or - value?

Answer 24

It has a negative value.

wmax = -n F Ecell = G

Question 25

What happens if G < 0 and Ecell > 0?

Answer 25

The reaction is spontaneous

Question 26

Does large K correspond to a large positive Ecell?

Answer 26

Yes

Question 27

What is electrolysis?

Answer 27

When electrical energy drives a nonspontaneous reaction to occur.

Question 28

What is “overpotential” required for?

Answer 28

It is required to overcome interactions at the surface of the electrode.

Question 29

If you know the time and the current of a cell you can determine what?

Answer 29

The number of electrons transferred in a redox reaction.

Question 30

What is an example of electrolysis?

Answer 30

Electrolysis of molten NaCl

At high temperatures, ionic solids melt to form liquids that conduct electricity.