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Chapter 30: Electrochemistry
Terms in this set (40)
What is the study of electrochemistry?
study of the relationship between chemical reactions and electrical energy
What are two types of electrochemical reactions? How do they produce a chemical change? What do both reactions involve?
spontaneous reaction that produces electrical energy nonspontaneous reaction that uses electrical energy
a transfer of electrons through the process of oxidation and reduction
What reactions occur in electrochemical cells? What are two types of cells? What kind of reactions occur in each cell?
redox reaction, which proviides energy
galvanic cells: spontaneous reactions
electrolytic cells: nonspontaneous reactions
How do you remember which electrodes do what in an electrochemical cell?
AN OX and a RED CAT
Anode is the side of OXdidation
Reduction occurs at the CAThode
What is the Gibbs free energy sign in a redox reaction occurring in a galvanic cell? Why? How is this energy harnessed?
it is spontaneous
oxidation and reduction half-reactions are placed in separate containers that are connected by an apparatus that allows the flow of electrons between them
the two parts of an electrochemical cell in which the separate oxidation and reduction reactions occur
What charge begins to build up in what electrode in the solution in half-cells? Why? How can this be prevented?
negative around the cathode
the flow of electrons is away from the anode and towards the cathode
a salt bridge or semipermeable membrane lets cations and anions exchange with each other
Why do electrochemical cells last for a short time?
the flow of electrons depletes the salt bridge
_____ flow to the cathode, and ____ flow to the anode.
What are the three rules in constructing a cell diagram?
1. reactants and products are always listed from left to right: anonde | anode solution || cathode solution | cathode
2. a single vertical line indicates a phase boundary
3. a double vertical line indicates a salt bridge
What is the Gibbs free energy sign in a redox reaction occurring in an electrolytic cell? Why? Are there half-cells used? Why or why not?
electrical energy is needed to induce the reaction
no, the reaction is nonspontaneous
What drives an electrolytic cell?
a battery or power source
What is the way to remember which way electrons flow in an electrochemical cell?
From anode to cation
What is the charge on the anode of an electrolytic cell? Why? What is the charge on the anode of a galvanic cell? Why?
attached to the positive pole of the battery
spontaneous oxidation reaction in the anode is the original source of the cell's negative charge
How is charge created in a galvanic vs. electrolytic cell?
galvanic: spontaneously created as electrons are released by oxidizing species at the anode
electrolytic: electrons are forced through the cathode, where they encounter the oxidizing agents
What is electrophoresis? What can electrophoresis be used for?Where do amino acid cations and anions travel towards and how are they deprotonated/protonated?
a technique used to separate amino acids based on their isoelectric points
separate proteins and DNA
amino acid cations: pronated at the pH of the solution and travel towards cathode
amino acid anions: deprotonated at the solution pH and travel towards anode
What is the balanced, general reaction to find the number of moles exchanged in an electrochemical cell?
M^(n+) + ne^- -> M
M = number of moles
n = electrons transferred per atom in moles
What is the equation used to determine the number of moles of electron transferred by an electrochemical cell?
I multiplied by t = n multiplied by F
I = current in amps
t = time in seconds
n = number of moles of electrons
F = faraday constant
How many moles of solid copper are produced during a redox reaction that generates 4 Amps of current for three seconds according to the reaction:
Zn + Cu 2+ -> Zn 2+ + Cu
it = Fn
n = (it)/F
n = (4)(3) / 10^5
= 1.2 * 10^-4 mole of electrons
Copper is reduced from Cu 2+ to Cu, which requires to electrons: Cu 2+ + 2e- -> Cu
(1 mol Cu/2 mol e-) = 6 * 10^-5 mol Cu
What does the reduction potential of each species determine? What is its definition?
the species in a redox reaction that will be oxidized or reduced
the tendency of a species to acquire electrons and be reduced
Is reduction potential intrinsic?
The more ____ the potential, the greater the tendency to be reduced.
What is a reduction potential defined relative to?
standard hydrogen electrode
How is standard reduction potential measured? List each of these conditions.
under standard conditions
1 M concentration for each ion participating in reaction, 25 C, a partial pressure of 1 atm for each gas, metals in their pure state
A higher standard reduction potential (Eo) means a _____ tendency for reduction to occur, while a lower Eo means a _____ tendency for oxidation.
When two half-reactions occur in the same system, the half-reaction with the _____ reduction potential will occur in reverse as an oxidation.
Given the following half-reactions and Eo values, determine which species would be oxidized and which would be reduced. What would the net redox reaction equation be? What would happen to the signs of Eo?
Ag + (aq) + e- -> Ag(s) Eo = +0.8V
TI+ (aq) + e- -> TI (s) Eo = -0.34 V
Since Ag + (aq) has the higher Eo, Ag + would be reduced to Ag and TI+ would be oxidized
Ag+ (aq) + TI (s) -> TI+ (aq) + Ag (s)
the signs would be reversed so the oxidation half reaction would be Eo = +0.34 V and the reduction would be Eo = -0.8 V
What is the standard electromotive force (Eocell)? How is it determined?
difference in potential between two half cells
adding the standard reduction potential of the reduced species and the standard oxidation potential of the oxidized species
The standard Eocell of a galvanic cell is _______, and the standard Eocell of an electrolytic cell is _______.
Given that the standard reduction potentials for Sm 3+ and RhCl6 3- are -2.41 V and +0.44 V, calculate the Eocell of the following reaction:
Sm 3+ + Rh + 6 Cl- -> RhCl6 3- + Sm
What kind of cell is this? Which direction would it spontaneously occur in? How does this change Eocell?
Rh is oxidized and Sm is reduced
Eocell = -2.41 + 0.44 = -2.85 V
to the left because Sm would be oxidized
it makes it +2.85 V
The signs of Gibb's free energy and Eocell are ______.
A ______ cell has a negative delta G and a positive Eocell, and a ______ cell has a positive delta G and a negative Eocell
What is Keq when products are favored over reactions? What does this say about the spontaneity of the forward/reverse reaction? What is delta G?
Keq > 1
forward reaction is spontaneous
What is Keq when reactants are favored over products? What does this say about the spontaneity of the forward/reverse reaction? What is delta G?
Keq < 1
reverse reaction is spontaneous
How can the effect of concentration on Eocell be calculated? What is Q?
Ecell = Eocell - (RT/nF) (ln Q)
if aA + bB --> cC + dD, then
Q = ([C]^c + [D]^d)/([A]^a + [B]^b)
Q is the reaction quotient for a given reaction
If one farad is equivalent to 96487 C/mol e-, what is the charge of an individual electron?
1 mol e-
(mol e- / 6
10^23) * (10^5 C/mol e-)
= 1.67 * 10^-19 C
If one farad is equivalent to 96487 C/mol e-, how many farads are required for the reduction of one mole of Ni 2+ (aq) to Ni (s)?
How many coulombs would be required to plate 0.6 grams of Au onto a metal? Au 3+ + 3 e- --> Au
0.6 g * (1 mol Au/197 g) = 0.003 mol Au
0.003 mol Au * (3 mol e-/1 mol Au) = 0.009 mol e-
0.009 mol e-
(10^5 C/mol e-) = 9
What is the standard emf if
Co 3+ -> Co 2+ Eo = +1.82
Na+ --> Na Eo = -2.71
emf = reduction + oxidation
=1.82 + 2.71 = 4.53 V
What is the Eocell for a reaction in which delta G = -553.91 kJ and two electrons are transferred?
Eocell = -G/nF
= 3 V
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