Ch. 12: Electrochemistry Flashcards
List the 3 types of electrochemical cells.
Galvanic, electrolytic, and concentration
What type of reactions do galvanic, electrolytic, and concentration cells house?
Galvanic and concentration: spontaneous reactions
Electrolytic: non-spontaneous reactions
What are electrodes?
Site where oxidation or reduction takes place
What reaction occurs at the anode vs the cathode?
Oxidation occurs at anode. Reduction occurs at cathode.
AN OX
RED CAT
What is emf? How does it relate to Gibb’s free energy?
Emf is the electron motive force, which corresponds to the voltage or electrical potential difference of the cell.
If emf is POSITIVE, then ΔG is NEGATIVE.
If emf is NEGATIVE, then ΔG is POSITIVE.
Which way do electrons move in an electrochemical cell?
Anode to cathode
Which way does current run?
Cathode to anode
CURRENT CATHODE
What is the function of a salt bridge?
It permits the exchange of cations and anions that do not react with the electrodes or ions in solution. This is needed to dissipate newly generated charges. If too much positive charge builds up on the anode and too much negative charge on the cathode then current will eventually cease.
What does the double vertical line || indicate in a cell diagram?
Presence of salt bridge
What does a single vertical line indicate in a cell diagram?
Indicates a phase boundary
Zn (s) | Zn2+ (aq)
What is listed on the left side of the cell diagram shorthand?
Anode
anode | anode solution (concen.) || cathode | cathode solution (concen.)
What is the ΔG of an electrolytic cell?
POSITIVE because it is non-spontaneous
How are non-spontaneous reactions in an electrolytic cell driven forward?
By an external voltage change (battery)
What is Faraday’s Law?
The liberation of gas and deposition of elements on electrodes is directly proportional to the number of electrons being transferred during the oxidation-reduction reaction.
What is Faraday’s constant?
1 F = 10^5 C/mol e-
charge per mol of electrons
What is the electrodeposition equation?
mol M = It/nF
mol M is amount of metal ion deposited at electrode
I is current
t is time
n is number of electron equivalents for metal ion
F is Faraday’s constant
How is emf calculated?
E°cell = E° (red,cathode) - E° (red,anode)
Describe the design of a concentration cell.
The electrodes are chemically identical and connected by a conductive material.
What is isolelectric focusing?
A technique used to separate amino acids or polypeptides based on their isoelectric points (pH at net neutral charge)
What does a more positive E°red mean?
Greater relative tendency for reduction to occur
How do you determine which electrode is the cathode vs anode based on reduction potential for a galvanic cell?
The electrode with the more positive E° is the cathode because this is where reduction occurs. The less positive E° is the anode.
What is considered the negative electrode in a galvanic vs electrolytic cell? Why?
Galvanic: anode because it is the source of electrons
Electrolytic: cathode because it is attached to the positive pole of the external voltage source and attracts anions
What is considered the positive electrode in a galvanic vs electrolytic cell?
Galvanic: cathode
Electrolytic: anode
Are cations attracted to the cathode or anode?
Cathode because that is where reduction takes place
Are anions attracted to the cathode or anode?
Anode because that is where oxidation takes place.
How do you determine which electrode is the cathode vs anode based on reduction potential for an electrolytic cell?
The electrode with the more positive reduction is forced by the external voltage source to be oxidized and is, therefore, the anode.
The electrode with the less positive reduction potential is forced to be reduced and is, therefore, the cathode.
What is the equation that relates ΔG and E°cell?
ΔG = - nFE°cell NOTICE THE NEGATIVE SIGN
n is # of moles of electrons
F is Faradays constant (10^5)
What is the Nernst equation and when is it used?
Ecell = E°cell - (RT/nF) ln Q
This equation is used when conditions deviate from standard conditions (298 K, 1 M, 1 atm)
What is the Nernst equation assuming 298K conditions?
Ecell = E°cell - (0.0592/n) log Q
If Keq is greater than 1, what is E°cell and ΔG?
If Keq is greater than 1 then products are favored. E°cell will be positive and ΔG will be negative.
If Keq is less than 1, what is E°cell and ΔG?
If Keq is less than 1 then reactants are favored. E°cell will be negative and ΔG will be positive.
What equation relates ΔG and Q?
ΔG = ΔG° + RT ln Q
