Chapter 17: Electrochemistry

Question 1

what is electrochemistry

Answer 1

branch of chemistry that relates electricity and chemical reactions

Question 2

what is the easiest method to use when balancing redox rxns

Answer 2

half-reaction method

Question 3

what is the half-reaction method

Answer 3

1. write the oxidation and reduction rxns as separate processes
2. balance the 1/2 reactions then combine them

Question 4

what do you have to do to balance a reaction that occurred in a basic solution?

Answer 4

• add OH- to each side and neutralize the H+ and this will create h2O

Question 5

what is another name for a voltaic cell and what is it

Answer 5

• separate redox reactions to create a flow of electrons
• galvanic cell and it means spontaneous

Question 6

what is a half cell

Answer 6

two metals that are not in direct contact with one another

Question 7

what is an electrode, where does oxidation occur, and where does reduction occur?

Answer 7

1. two solid metals that are connected by an external circuit
2. oxidation happens at the anode
3. reduction happens at the cathode

Question 8

where do electrons flow in a voltaic cell

Answer 8

1. from anode to the cathode

Question 9

what happens as electrons leave the anode

Answer 9

1. cations dissolve into the solution of the anode compartment
2. anode loses mass, the solution becomes more concentrated

Question 10

what happens the cathode as electrons enter it

Answer 10

1. cations in the solution are attracted to the negative cathode
2. electrons transfer the cations forming neutral metals
3. cathode gains mass and the solution becomes less concentrated

Question 11

what is a salt bridge and what would happen if we didn’t have one

Answer 11

• u shaped tube that contains salt solution to keep the charges balanced

if we didn’t have a salt bridge the charges would not be balanced and the flow of electrons would stop

Question 12

what ions are a salt bridge composed of

Answer 12

ions that will not react with the other ions in the cell or with the elctrode

Question 13

where do anions move towards

where do cations move towards

Answer 13

1. move toward the anodes (-)
2. move toward the cathode (+)

Question 14

what is cell notation

Answer 14

• shorthand description of a voltaic cell

electrode| electrolyte || electroltye|| electrode

Question 15

what does | mean in a voltaic cell

what does || mean

what does , mean

Answer 15

1. phase barrier
2. || = salt bridge
3. = ,= used if multiple electrolytes are in the same phase

Question 16

what direction do electrons flow spontaneously

Answer 16

in one way bc of the difference in potential energy

flow from the anode to the cathode bc the PE of electrons is higher in the anode than the cathode

Question 17

what is potential difference

Answer 17

the difference in PE per electrical charge

Question 18

what is the electromotive force (emf)

units = Volts or V

Answer 18

the potential difference in a cell between the anode and cathode

• it is also called the Ecell

Question 19

what is a voltmeter and how does it work

Question 20

what will the cell potential be for a spontaneous reaction

Answer 20

cell potential will be positive because Ecell is measured in volts

Question 21

what does emf of a voltaic cell depend on

Answer 21

the cathode and anode half cells involved

emf is also called cell voltage

Question 22

what is the oxidzing agent

what is the reducing agent

Question 23

what does Ered refer to

Answer 23

the standard conditions for the electrode for reduction reactions

Question 24

what is the standard hydrogen electrode (SHE)

Answer 24

• the reduction of H+ to H2 under standard conditions

H2 (g) at 1 atm and and an acidic solution with [H+] = 1M

Question 25

how many volts does SHE equal

Answer 25

0 V

Question 26

what does SHE consist of

Answer 26

an electrode with a finely divided Pt(platinum) in contact with H2

Question 27

what happens when SHE is the cathode

what happens when SHE is the anode

Answer 27

1. cathode of a cell then the two H+ ions each accept an electron from the Pt electrode and are reduced to H atoms
2. anode H2 molecules lose two electrons and are oxidized to H+

Question 29

why is standard potential an extensive property

Answer 29

it is based the amount of energy per unit of charge

increase the substances then we would increase the energy

Question 30

what is the standard cell potential equation

Answer 30

Ecell = Ered(cathode / reduction)+ -(red(anode/ oxidation))

Question 31

what is the Ered for strong oxidizers

Answer 31

• the strongest oxidizers have the most positive Ered
• have a greater tendency for the reactant of the 1/2 rxn to be reduced and oxidize another species

Question 33

what is the E red for strong reducers

Answer 33

• they have the most negative E red
• half rxn w/ the smallest Ered is the most easily reversed as an oxidation

Question 34

Ered =

Answer 34

red(red)-red(ox)

Question 35

what is the equation for cell potential and electric work

Answer 35

E = -w/q and q = nF

q = quantity of charge in C transferred

n = moles of electrons

F = faraday = 96485 C/mol e^-

Question 36

how is work related to free energy

Answer 36

G = wmax = -qEmax = -nFE

Question 37

what happens as a voltaic cell is discharged

Answer 37

the reactants are consumed and the products are produced

* the concentrations of the reactants and products are not constant*

emf = 0 meaning it is considered dead and it is at equilibrium

Question 38

what is the nernst equation

Answer 38

emf generated under nonstandard conditions can be calculated using the nernst equation

Question 39

what is the nernst equation

Answer 39

E = 0.0592V/ n logk

Question 40

what are the conditions for a spontaneous rxn

Answer 40

G = negative

K = positive

E = positive